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BRITISH STANDARD BS 57:1951Incorporating Amendment Nos. 1, 2 and 3

Specification for

B.A. Screws bolts and nuts

UDC 621.882.082.1(42)

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BS 57:1951

This British Standard, having been approved by the Mechanical Engineering Industry Standards Committee and endorsed by the chairman of the Engineering Divisional Council, was published under the authority of the General Council on31 March 1951

© BSI 09-1999

First published 1920First revision September 1944Second revision March 1951

ISBN 0 580 00920 3

Co-operating organizations

The Mechanical Engineering Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations:—

Admiralty* Institute of PetroleumAir Ministry Institution of Civil EngineersAssociation of Consulting Engineers Institution of Gas Engineers

(Incorporated) Institution of Heating and VentilatingAssociated Offices Technical Committee EngineersBritish Chemical Plant Manufacturers’ Institution of Mechanical Engineers

Association Institution of Mechanical EngineersBritish Compressed Air Society (Automobile Division)British Electrical and Allied Manufacturers’ Institution of Production Engineers*

Association* Locomotive Manufacturers’ Association*British Engineers’ Association* Machine Tool Trades Association*British Internal Combustion Engine Ministry of Fuel and Power

Manufacturers’ Association* Ministry of Labour and National ServiceBritish Iron and Steel Federation* (Factory Department)British Railways, The Railway Executive* Ministry of Supply*Crown Agents for the Colonies* Ministry of Transport*Department of Scientific and Industrial Ministry of Works

Research Office of the High Commissioner for India*Engineering Equipment Users’ Association* War OfficeInstitute of Marine Engineers

The Government departments and scientific organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard:—

Aircraft Bolt and Nut Manufacturers Metal Thread Screw Manufacturers’Association Association (Rolled Screw Section)

Bright Bolt and Nut Manufacturers Metal Thread Screw Manufacturers’Association Association (Turned Screw Section)

Bright Steel Bar Association National Physical LaboratoryBritish Constructional Steelwork Association Oil Companies Materials CommitteeBritish Cycle and Motor Cycle Manufacturers’ Radio Industry Council

and Traders’ Union Ltd Society of British Aircraft ConstructorsBritish Steel Wire Industries Association Society of Motor Manufacturers andCold Headed Heat-treated Bolt Association Traders Ltd.Council of British Manufacturers of Petroleum Telecommunications, Engineering and

Equipment Manufacturing AssociationGeneral Post Office Washer Manufacturers’ AssociationInstitution of Naval Architects

Amendments issued since publication

Amd. No. Date of issue Comments

4329 October 1961

5901 August 1966

1528 August 1974 Indicated by a sideline in the margin

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BS 57:1951

© BSI 09-1999 i

Contents

PageCo-operating organizations Inside front coverForeword iiSection 1. Screws, bolts and nuts1 Scope 12 Method of manufacture 13 Material 14 Dimensions 15 Length of screws and bolts 16 Ends of screws and bolts 17 Screw threads 28 Length of thread on screws and bolts 29 Chamfering and washer-facing 3Section 2. Plain washersDeletedAppendix A Special types of screws not normally stocked 14Appendix B Approximate proportions 16Appendix C Metric slot widths 16Figure 1 — Alternative types of ends permissible on screws and bolts 2Figure 2 — Cheese head screw 4Figure 3 — Round head screw 5Figure 4 — Countersunk head screw 6Figure 5 — Raised-countersunk head screw 7Figure 6 — Hexagonal headed screw 8Figure 7 — Hexagonal headed bolt 8Figure 8 — Washer faced head 8Figure 9 — Hexagonal ordinary nut 9Figure 10 — Hexagonal thin (or lock) nut 9Figure 11 — Hexagonal ordinary nut 9Figure 14 — Raised cheese (fillister) head screw 14Figure 15 — Connection head screw 15Table 1 — Cheese head screws 4Table 2 — Round head screws 5Table 3 — Countersunk head screws 6Table 4 — Raised-countersunk (instrument) head screws 7Table 5 — Hexagonal headed screws and bolts 8Table 6 — Hexagonal ordinary (or full) and thin (or lock) nuts 9Table 7 — Lengths of steel and brass cheese and countersunkhead B.A. screws (screwed to head) 10Table 8 — Lengths of steel and brass round head B.A. screws(screwed to head) 11Table 9 — Lengths of steel and brass raised-countersunk(instrument) head B.A. screws (screwed to head) 12Table 10 — Lengths of steel hexagonal head B.A. screws(screwed to head) and bolts (2 B.A. only) 13Table 13 — Raised cheese (fillister) head screws 14Table 14 — Connection head screws 15Table 15 — Slot widths 17NOTE The requirements for washers in this standard have been superseded by the publication of BS 3410, “Metal washers for general engineering purposes”, to which reference should now be made.

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BS 57:1951

ii © BSI 09-1999

Foreword

This standard requires reference to the following:—BS 93:1951, British Association (B.A.) screw threads, with tolerances for sizes 0 B.A. to 16 B.A.BS 4183:1967, Machine screws and machine screw nuts — metric series.This British Standard was first issued in 1920. The provisions of that edition related solely to the dimensions of the heads of the various types of screws and the dimensions of ordinary hexagon nuts.When the first revision of the standard was published in 1944 its scope was extended to include requirements for the complete dimensions of screws, bolts and nuts; in addition, dimensions for lock nuts and for two sizes of washers were given. The edition was issued as a War Emergency British Standard and took into account recommendations, contained in instructions issued by the Ministry of Supply, which indicated those types, sizes and lengths of small screws and bolts regarded as standard production.General dimensions for all the common types and sizes of B.A. screws bolts and nuts were included in the standard, but the dimensions for types not recognized as standard were given in an Appendix. The tables in the body of the specification designated selected sizes as “standard” and all other sizes as “specials”. A table of “Standard lengths of steel and brass B.A. bolts and screws for wartime production” was given in an Appendix.The War Emergency edition has now been reviewed in the light of present-day conditions and, whilst the principles stated above have been largely adopted in the present revision, certain modifications which more recent experience has shown to be desirable have been incorporated. There has been some rearrangement of the tables of general dimensions, including the transfer of the table of dimensions for “Raised-countersunk (instrument) head screws and bolts” from the Appendix to the body of the standard. The ranges of nominal sizes given in these tables are now designated “Preferred,” “Second choice” and “Not normally stocked”; the table of standard lengths has been reviewed and tables are now included in the standard relating to each type of screw and showing the lengths in which each size is normally stocked and other lengths which may be regarded as standard, although they are not normally stocked.Finally, since the production of B.A. bolts is very small compared with that of B.A. screws, the title of the standard has been suitably revised.A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pagesThis document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 17 and a back cover.This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.

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BS 57:1951

© BSI 09-1999 1

Section 1. Screws, bolts and nuts

1 ScopeSection 1 of this British Standard specifies requirements and dimensions for both ferrous and non-ferrous screws, bolts and nuts.

2 Method of manufactureScrews and bolts may be either turned from bars or forged.

3 MaterialThe material from which the screws, bolts and nuts are manufactured shall have an ultimate tensile stress of not less than the following:—

If the purchaser requires the screws, bolts and nuts to be manufactured from steel or brass of a higher tensile stress, or of another material, he shall specify the ultimate tensile stress of the material.NOTE The choice of alloy should normally be left to the manufacturer, but among suitable light alloys satisfying the requirement are the following:—For screws, bolts and nuts turned from wire or from the bar: BS 1475 or BS 1476 respectively:

4 DimensionsThe screws, bolts and nuts shall conform to the dimensions and tolerances given in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 13 and Table 14, and Clauses 5, 6, 7, 8 and 9.The screw heads shall be concentric with the shank. The slots shall be clean and free from burrs and, on visual inspection, shall appear to be closelyco-incident with the centre line of the head.NOTE Screws and bolts turned from bars can be supplied with a smaller radius under the head if specially ordered.

5 Length of screws and boltsa) Countersunk heads. The nominal length shall be the distance from the upper surface of the head to the extreme end of the shank, including any chamfer or radius.b) Raised-countersunk (instrument) heads. The nominal length shall be the distance from the upper surface of the head (excluding the raised portion) to the extreme end of the shank, including any chamfer or radius.c) Hexagonal, round, cheese, raised-cheese (fillister), and connection heads. The nominal length shall be the distance from the underside of the head to the extreme end of the shank, including any chamfer or radius.NOTE The nominal lengths of screws normally stocked are given in Table 7, Table 8, Table 9 and Table 10. Bolts (screwed part way) are not normally stocked but should be ordered to the lengths given in Table 7, Table 8, Table 9 and Table 10.

d) Tolerance on length. The permissible tolerance on the nominal length of screws and bolts shall be as follows:—

6 Ends of screws and boltsa) Cut threads. The ends of screws and bolts with cut threads may, at the option of the manufacturer, be finished with either a flat chamfer with a 90° included angle to a depth slightly exceeding the depth of thread, or with a radius approximately equal to 1¼ times the nominal diameter of the shank.b) Rolled threads. When screws and bolts are made with rolled threads the lead formed at the end of the screw or bolt by the thread-rolling operation may be regarded as providing the necessary chamfer to the end and no other machining operation is necessary, unless the purchaser, in his enquiry and order, has specified that the ends shall be finished as in Clause 6 a) above.NOTE For convenience, one type of end only is illustrated in the Figures at the head of Table 1 to Table 5 inclusive, and Table 13 and Table 14. The three alternative types of end permissible are shown in Figure 1 below.

Steel 25 tons/sq. in.Brass 20 tons/sq. in.Aluminium alloy 20 tons/sq. in.

BS 1475, “Aluminium and aluminium alloy wire for general purposes.”

H.G. 14. T

H.G. 15 (Condition W or WP)

BS 1476, “Aluminium and aluminium alloy rods, bars and sections for general purposes.”

H.E. 11. WP

H.E. 14. T

H.E. 15 (Condition W or WP)

For screws and bolts cold headed from wire:

BS 1475, “Aluminium and aluminium alloy wire for general purposes.”

N.G. 6. M

H.G. 14. T

H.G. 15 (Condition W or WP)

Nominal length Tolerance

Up to and including (in. + 0.01 in. – 0.Above ( in., up to andincluding " in. + 0.02 in. – 0.Above " in. + 1/32 in. – 0.

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BS 57:1951

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7 Screw threadsa) Screws and bolts. The screw threads may be either cut or rolled, at the option of the manufacturer. Limits and tolerances shall be as specified for normal class bolts in BS 93:1951, “British Association screw threads.” Screws and bolts with close class threads are not normally stocked and should not be ordered, except for special work where refined accuracy of pitch and thread form is particularly required. If the limits and tolerances in respect of the screws and bolts are to be as specified for close class bolts in BS 93:1951, this shall be stated by the purchaser in his enquiry and order.b) Nuts. The limits and tolerances of the screw threads shall be as specified in BS 93:1951.

8 Length of thread on screws and boltsa) Screws: countersunk and raised-countersunk heads. These shall be threaded right up to the head.

b) Screws: hexagonal, round, cheese, raised-cheese (fillister) and connection heads. These shall be threaded to leave a limited length of unthreaded shank under the head. The length of unthreaded shank is defined as the distance from the leading face of a nut which has been screwed as far as possible on to the screw by hand to the underside of the head. The nut shall have threads as specified in Clause 7 b) and shall not be countersunk.The length of unthreaded shank shall not exceed the following:—

c) Bolts. The length of thread on bolts shall be the distance from the end of the bolt (including any chamfer or radius) to the leading face of a nut which has been screwed as far as possible on to the bolt by hand. The nut shall have threads as specified in Clause 7 b) and shall not be countersunk.

Figure 1 — Alternative types of ends permissible on screws and bolts

Nominal length ofscrew

Length of unthreaded shank

Up to and including 5 times the diameter.

Not to exceed 1½ times the pitch.

Greater than 5 times the diameter.

Not to exceed 2½ times the pitch.

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BS 57:1951

© BSI 09-1999 3

The length of thread shall be not less than three times the nominal diameter of the bolt.

9 Chamfering and washer-facinga) Hexagonal headed screws and bolts. These shall have a chamfer of approximately 30° on their upper faces. The underside of the head may, at the option of the manufacturer, be finished flat, or in the case of sizes 0 to 6 B.A. inclusive, have a washer-face.

b) Hexagonal ordinary (or full) nuts. These shall have a chamfer of approximately 30° on both faces, but sizes 13 B.A. and smaller may, at the option of the manufacturer, be chamfered on one face only.c) Hexagonal thin (or lock) nuts. These shall have a chamfer of approximately 30° on both faces.

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BS 57:1951

4 © BSI 09-1999

Table 1 — Cheese head screws

Figure 2 — Cheese head screw1 2 3 4 5 6 7 8 9 10 11 12

B.A. No.

Diameter of shank and major

diameter of thread

Diameter of head Depth of head

Radius under head

Slot

Width Depth

D A B R H J

max. max. min. max. min. max. max. min. nom.

mm. in. in. in. in. in. in. in. in. in.

Preferred

246

81012

4.73.62.8

2.21.71.3

0.1850.1420.110

0.0870.0670.051

0.3190.2520.194

0.1570.1120.095

0.3090.2420.184

0.1470.1070.090

0.1300.1010.078

0.0630.0450.038

0.1230.0950.073

0.0590.0410.035

0.0150.0100.010

0.0100.0070.005

0.0520.0400.033

0.0300.0240.020

0.0440.0340.027

0.0240.0190.015

0.0580.0450.035

0.0270.0200.017

Second choice

0a

13

5

6.05.34.1

3.2

0.2360.2090.161

0.126

0.4130.3660.283

0.221

0.4030.3560.273

0.211

0.1670.1480.113

0.088

0.1590.1410.107

0.083

0.0150.0150.015

0.010

0.0640.0580.047

0.040

0.0560.0500.039

0.034

0.0750.0660.051

0.040

Not normally stocked

79

11

131415

16

2.51.91.5

1.21.00.9

0.79

0.0980.0750.059

0.0470.0390.035

0.031

0.1730.1280.110

0.0810.0640.064

0.058

0.1830.1230.105

0.0760.0590.059

0.054

0.0690.0520.045

0.0320.0260.026

0.023

0.0640.0480.041

0.0290.0230.023

0.020

0.0100.0070.005

0.0050.0030.003

0.003

0.0330.0300.024

0.0200.0150.015

0.013

0.0270.0240.019

0.0150.0110.011

0.009

0.0310.0240.020

0.0140.0120.012

0.010NOTE If the slot is produced by plunge milling, dimension J is measured from the upper surface of the head to the point at which the slot breaks out on the surface of the head.a It is recommended that ¼ in. B.S.F. screws to BS 450, “Bright countersunk, round and cheese head screws (B.S.W. and B.S.F.),” be used in preference to O.B.A.

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BS 57:1951

© BSI 09-1999 5

Table 2 — Round head screws

Figure 3 — Round head screw1 2 3 4 5 6 7 8 9 10 11 12 13

B.A. No.

Diameter of shank and

major diameter of thread

Diameter of head Depth of head

Radius under head

Radius of head

Slot

Width Depth

D A B R F H J

max. max. min. max. min. max. approx. max. min. nom.

mm. in. in. in. in. in. in. in. in. in. in.

Preferred

246

810

4.73.62.8

2.21.7

0.1850.1420.110

0.0870.067

0.3190.2520.194

0.1570.112

0.3090.2420.184

0.1470.107

0.1300.1010.078

0.0630.045

0.1230.0950.073

0.0590.041

0.0150.0100.010

0.0100.007

0.3190.2520.194

0.1570.112

0.0520.0400.033

0.0300.024

0.0440.0340.027

0.0240.019

0.0710.0560.043

0.0350.025

Second choice

0a

13

5

6.05.34.1

3.2

0.2360.2090.161

0.126

0.4130.3660.283

0.221

0.4030.3560.273

0.211

0.1670.1480.113

0.088

0.1590.1410.107

0.083

0.0150.0150.015

0.010

0.4130.3660.283

0.221

0.0840.0580.047

0.040

0.0560.0500.039

0.034

0.0920.0810.062

0.048

Not normally stocked

79

11

121314

1516

2.51.91.5

1.31.21.0

0.90.79

0.0980.0750.059

0.0510.0470.039

0.0350.031

0.1730.1280.110

0.0950.0810.064

0.0640.058

0.1630.1230.105

0.0900.0760.059

0.0590.054

0.0690.0520.045

0.0380.0320.026

0.0260.023

0.0640.0480.041

0.0350.0290.023

0.0230.020

0.0100.0070.005

0.0050.0050.003

0.0030.003

0.1730.1280.110

0.0950.0810.064

0.0640.058

0.0330.0300.024

0.0200.0200.015

0.0150.013

0.0270.0240.019

0.0150.0150.011

0.0110.009

0.0380.0290.025

0.0210.0180.014

0.0140.013

NOTE 1 If the slot is produced by plunge milling, dimension J is measured from the upper surface of the head to the point at which the slot breaks out on the surface of the head.NOTE 2 Shape of head. The shape of the head shall closely approximate to a half-ellipse Radius G (struck off the underside of the head) must pass through diameter A and touch radius F.a It is recommended that ¼ in. B.S.F. screws to BS 450, “Bright countersunk, round and cheese head screws (B.S.W. and B.S.F.),” be used in preference to O.B.A.

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BS 57:1951

6 © BSI 09-1999

Table 3 — Countersunk head screws

Figure 4 — Countersunk head screw1 2 3 4 5 6 7 8 9 10 11

B.A. No.

Major diameter of thread Diameter of head

Depth of head Slot

Total Width Depth

D A B E H J

max. max. min. nom. max. max. min. nom.

mm. in. in. in. in. in. in. in. in.

Preferred

246

81012

4.73.62.8

2.21.71.3

0.1850.1420.110

0.0870.0670.051

0.3190.2520.194

0.1570.1120.095

0.3090.2420.184

0.1470.1070.090

0.0770.0650.051

0.0430.0300.028

0.0100.0100.009

0.0080.0070.006

0.0520.0400.033

0.0300.0240.020

0.0440.0340.027

0.0240.0190.015

0.0360.0310.024

0.0210.0160.014

Second choice

0a

13

5

6.05.34.1

3.2

0.2360.2090.161

0.126

0.4130.3660.283

0.221

0.4030.3560.273

0.211

0.0990.0890.071

0.058

0.0100.0100.010

0.010

0.0640.0580.047

0.040

0.0560.0500.039

0.034

0.0450.0410.033

0.028

Not normally stocked

79

11

131415

16

2.51.91.5

1.21.00.9

0.79

0.0980.0750.059

0.0470.0390.035

0.031

0.1730.1280.110

0.0810.0640.064

0.058

0.1630.1230.105

0.0760.0590.059

0.054

0.0470.0350.033

0.0230.0190.021

0.019

0.0090.0080.007

0.0060.0060.006

0.005

0.0330.0300.024

0.0200.0150.015

0.013

0.0270.0240.019

0.0150.0110.011

0.009

0.0230.0180.016

0.0120.0110.011

0.010NOTE If the slot is produced by plunge milling, dimension J is measured from the upper surface of the head to the point at which the slot breaks out on the surface of the head.a It is recommended that ¼ in. B.S.F. screws to BS 450, “Bright countersunk, round and cheese head screws (B.S.W. and B.S.F.),” be used in preference to O.B.A.

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BS 57:1951

© BSI 09-1999 7

Table 4 — Raised-countersunk (instrument) head screws

Figure 5 — Raised-countersunk head screw1 2 3 4 5 6 7 8 9 10 11 12 13

B.A. No.

Major of diameter of

thread

Diameter of head Depth of head Radius

Slot

Width Depth

D A E B M F H J

max. max. min. max. nom. approx. nom. max. min. nom.

mm. in. in. in. in. in. in. in. in. in. in.

Preferred

246

810

4.73.62.8

2.21.7

0.1850.1420.110

0.0870.067

0.3190.2520.194

0.1570.112

0.3090.2420.184

0.1470.107

0.0100.0100.009

0.0080.007

0.0770.0650.051

0.0430.030

0.0360.0290.023

0.0190.013

0.3700.2830.220

0.1730.134

0.0520.0400.033

0.0300.024

0.0440.0340.027

0.0240.019

0.0590.0490.039

0.0330.024

Not normally stocked

0a

13

579

111213

141516

6.05.34.1

3.22.51.9

1.51.31.2

1.00.90.79

0.2360.2090.161

0.1260.0980.075

0.0590.0510.047

0.0390.0350.031

0.4130.3660.283

0.2210.1730.128

0.1100.0950.081

0.0640.0640.058

0.4030.3560.273

0.2110.1630.123

0.1050.0900.076

0.0590.0590.054

0.0100.0100.010

0.0100.0090.008

0.0070.0060.006

0.0060.0060.005

0.0990.0890.071

0.0580.0470.035

0.0330.0280.023

0.0190.0210.019

0.0480.0420.035

0.0260.0220.014

0.0130.0120.009

0.0080.0080.006

0.4720.4170.323

0.2520.1970.150

0.1180.1020.094

0.0790.0710.062

0.0640.0580.047

0.0400.0330.030

0.0240.0200.020

0.0150.0150.013

0.0560.0500.039

0.0340.0270.024

0.0190.0150.015

0.0110.0110.009

0.0750.0670.056

0.0450.0370.027

0.0240.0220.018

0.0160.0160.013

NOTE If the slot is produced by plunge milling, dimension J is measured from the upper surface of the head to the point at which the slot breaks out on the surface of the head.a It is recommended that ¼ in. B.S.F. screws (which will be included in the revised BS 450) be used in preference to O.B.A.

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BS 57:1951

8 © BSI 09-1999

Table 5 — Hexagonal headed screws and bolts

Figure 6 — Hexagonal headed screw

Figure 7 — Hexagonal headed bolt Figure 8 — Washer faced headAlternative type of head permissible on screw and bolts, sizes 0 to 6 B.A. inclusive only [see Clause 9 a)].

1 2 3 4 5 6 7 8 9 10 11 12 13

B.A. No.

Diameter of shank and

major diameter of thread

Width across flats

Width across

corners

Thickness of head

Radius under head

Diameter of washer face

Length of

thread of bolts

D A E B R C L

max. max. min. max. max. min. max. max. min. min.

mm. in. in. in. in. in. in. in. in. in. in.

Preferred 24

4.73.6

0.1850.142

0.3240.248

0.3190.243

0.370.29

0.1390.106

0.1320.100

0.0150.010

0.3190.243

0.3090.233

0.550.43

Not normally stocked

0a

13

567

89

10

6.05.34.1

3.22.82.5

2.21.91.7

0.2360.2090.161

0.1260.1100.098

0.0870.0750.067

0.4130.3650.282

0.2200.1930.172

0.1520.1310.117

0.4080.3600.277

0.2160.1890.169

0.1490.1280.114

0.480.420.33

0.250.220.20

0.180.150.14

0.1770.1560.121

0.0940.0830.074

0.0650.0560.050

0.1690.1490.115

0.0890.0780.070

0.0610.0520.046

0.0150.0150.015

0.0100.0100.010

0.0100.0070.007

0.4080.3600.277

0.2160.189—

———

0.3980.3500.267

0.2060.179—

———

0.710.630.48

0.380.330.29

0.260.220.20

a It is recommended that ¼ in. B.S.F. screws and bolts to BS 1083, “Precision hexagon bolts, screws, nuts (B.S.W. and B.S.F. threads) and plain washers,” be used in preference to O.B.A.

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BS 57:1951

© BSI 09-1999 9

Table 6 — Hexagonal ordinary (or full) nuts and thin (or lock) nuts

Figure 9 — Hexagonal ordinary nut Figure 10 — Hexagonal thin (or lock) nut

Figure 11 — Hexagonal ordinary nutAlternative chamfering permissible on sizes 13 B.A. and smaller. [see Clause 9 b)].

1 2 3 4 5 6 7 8 9 10 11

B.A. No.

Nominal diameter of

threadWidth across flats

Width across

corners

Thickness

Ordinary (or full) nuts Thin (or lock) nuts

D A E B C

max. min. max. max. min. max. min.

mm. in. in. in. in. in. in. in. in.

Preferred

246

81012

4.73.62.8

2.21.71.3

0.1850.1420.110

0.0870.0670.051

0.3240.2480.193

0.1520.1170.090

0.3190.2430.189

0.1490.1140.088

0.370.290.22

0.180.140.10

0.1670.1350.105

0.0820.0640.049

0.1570.1250.095

0.0750.0570.044

0.1230.0940.073

0.058——

0.1130.0840.063

0.051——

Second choice

0a

13

5

6.05.34.1

3.2

0.2360.2090.161

0.126

0.4130.3650.282

0.220

0.4080.3600.277

0.216

0.480.420.33

0.25

0.2130.1880.153

0.120

0.2030.1780.143

0.110

0.1570.1390.108

0.084

0.1470.1290.098

0.074

Not normally stocked

79

11

131415

16

2.51.91.5

1.21.00.9

0.79

0.0980.0750.059

0.0470.0390.035

0.031

0.1720.1310.103

0.0830.0690.062

0.056

0.1690.1280.101

0.0810.0670.060

0.054

0.200.150.12

0.100.080.07

0.07

0.0940.0710.056

0.0450.0370.034

0.029

0.0870.0640.051

0.0400.0320.029

0.024

———

———

—

———

———

—a It is recommended that ¼ in. B.S.F. nuts to BS 1083, “Precision hexagon bolts, screws, nuts (B.S.W. and B.S.F. threads) and plain washers,” be used in preference to O.B.A.

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BS 57:1951

10 © BSI 09-1999

Table 7 — Lengths of steel and brass cheese and countersunk head B.A. screws(screwed to head)

Length in

inches

Preferred B.A. sizes Second choice B.A. sizes

B.A. sizes not normally stocked

2 4 6 8 10 12 0 1 3 5 7 9 11 13 14 15 16

1/16

5/643/32

7/641/85/32

3/167/321/45/163/87/16

1/29/165/83/47/8

1

11/811/413/8

11/213/42

1

1

112

1

1

111

212

122

1

1

112

1

1

111

212

2

1

1

1

112

121

122

222

2

1

1

1

112

121

122

1

11

121

112

121

2

1

1

11

121 2

2

2

2

222

222

222

2

2

2

2

222

222

222

2

2

222

2

2

222

222

2

2

2

222

2

2

222

222

2

3

3

3

333

333

333

3

3

3

333

333

3

3

3

33

333

3

3

3

333

3

3

3

3

333

3

3

3

3

33

3

3

3

33

NOTE 1 The column headings “Preferred,” “Second choice” and “Not normally stocked” refer to the B.A. sizes, which have been grouped in accordance with Table 1 and Table 3. For choice of lengths, see above.NOTE 2 Stock lengths are those shown as 1 and 2. They relate to screws having normal class threads; screws with close class threads are not normally stocked. The lengths shown as 1 are those normally stocked and should be used whenever possible; the lengths shown as 2 are less likely to be obtained immediately from stock than those shown as 1. The lengths shown as 3 are not normally stocked. Intermediate lengths not shown in the above table should be avoided.NOTE 3 Aluminium alloy cheese and countersunk head B.A. screws are not normally stocked.NOTE 4 Bolts (screwed part way) are not normally stocked and their use should be avoided. If required they should be ordered to the lengths shown in the table.

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BS 57:1951

© BSI 09-1999 11

Table 8 — Lengths of steel and brass round B.A. screws (screwed to head)

Length in

inches

Preferred B.A. sizes Second choice B.A. sizes

B.A. sizes not normally stocked

2 4 6 8 10 0 1 3 5 7 9 11 12 13 14 15 16

1/16

5/643/32

7/641/85/32

3/167/321/45/163/87/16

1/29/165/83/47/8

1

11/811/413/8

11/213/42

1

1

112

1

1

111

212

122

1

1

112

1

1

111

212

2

1

1

1

112

121

122

222

2

1

1

1

112

121

122

1

11

121

112

121

2

2

2

2

2

222

222

222

2

2

2

2

222

222

222

2

2

222

2

2

222

222

2

2

2

222

2

2

222

222

2

3

3

3

333

333

333

3

3

3

333

333

3

3

3

33

333

3

3

33

333

3

33

333

3

3

33

333

3

3

33

33

3

33

33

NOTE 1 The column headings “Preferred,” “Second choice” and “Not normally stocked” refer to the B.A. sizes, which have been grouped in accordance with Table 2. For choice of lengths, see above.NOTE 2 Stock lengths are those shown as 1 and 2. They relate to screws having normal class threads: screws with close class threads are not normally stocked. The lengths shown as 1 are those normally stocked and should be used whenever possible. The lengths shown as 2 are less likely to be obtained immediately from stock than those shown as 1. The lengths shown as 3 are not normally stocked. Intermediate lengths not shown in the above table should be avoided.NOTE 3 Aluminium alloy round head B.A. screws are not normally stocked.NOTE 4 Bolts (screwed part way) are not normally stocked and their use should be avoided. If required they should be ordered to the lengths shown in the table.

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BS 57:1951

12 © BSI 09-1999

Table 9 — Lengths of steel and brass raised-countersunk (instrument) head B.A. screws (screwed to head)

Length in

inches

Preferred B.A. sizes B.A. sizes not normally stocked

2 4 6 8 10 0 1 3 5 7 9 11 12 13 14 15 16

1/16

5/643/32

7/641/85/32

3/167/321/45/163/87/16

1/29/165/83/47/8

1

11/811/413/8

11/213/42

3

2

313

1

2

121

323

233

3

1

212

1

2

121

323

3

3

3

1

212

132

222

333

3

1

1

1

223

333

333

3

13

131

223

333

3

3

3

3

3

333

333

333

3

3

3

3

333

333

333

3

3

333

3

3

333

333

3

3

3

333

3

3

333

333

3

3

3

3

333

333

33

3

3

3

3

333

333

3

3

3

33

333

3

3

33

333

333

333

3

333

333

3

333

33

333

33

NOTE 1 The column headings “Preferred” and “Not normally stocked” refer to the B.A. sizes which have been grouped in accordance with Table 4. For choice of lengths, see above.NOTE 2 Stock lengths are those shown as 1 and 2. They relate to screws having normal class. threads: screws with close class threads are not normally stocked. The lengths shown as 1 are those normally stocked and should be used whenever possible. The lengths shown as 2 are less likely to be obtained immediately from stock than those shown as 1. The lengths shown as 3 are not normally stocked. Intermediate lengths not shown in the above table should be avoided.NOTE 3 Aluminium alloy raised-countersunk (instrument) head B.A. screws are not normally stocked.NOTE 4 Bolts (screwed part way) are not normally stocked and their use should be avoided. If required they should be ordered to the lengths shown in the table.

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BS 57:1951

© BSI 09-1999 13

Table 10 — Lengths of steel hexagonal head B.A. screws (screwed to head) and bolts (2 B.A. only)

Section 2. Plain washers

deleted

Length in inches

Preferred B.A. sizesB.A. sizes not normally stocked

2 B.A. 4 B.A.

Screws Bolts Screws 0 1 3 5 6 7 8 9 10

3/16

1/45/16

3/87/161/29/165/83/47/8

111/8

11/413/811/2

13/4221/4

21/2

322

121

11

213

131

22

1

313

131

222

2

312

121

11

213

132

22

3

3

3

33

333

333

33

3

3

3

33

333

333

33

333

333

33

333

333

333

333

33

333

333

333

333

333

333

333

333

333

333

33

333

333

333

33

333

333

333

333

333

333

NOTE 1 The column headings “Preferred” and “Not normally stocked” refer to the B.A. sizes which have been grouped in accordance with Table 5. For choice of lengths see above.NOTE 2 Stock lengths are those shown as 1 and 2. They relate to screws and bolts having normal class threads: screws and bolts with close class threads are not normally stocked. The lengths shown as 1 are those normally stocked and should be used whenever possible. The lengths shown as 2 are less likely to be obtained immediately from stock than those shown as 1. The lengths shown as 3 are not normally stocked. Intermediate lengths not shown in the above table should be avoided.NOTE 3 Brass and aluminium alloy hexagonal head B.A. screws and bolts are not normally stocked.NOTE 4 With the exception of certain lengths of 2 B.A. bolts (shown in Table 10 above), bolts (screwed part way) are not normally stocked and their use should be avoided. If required they should be ordered to the lengths shown in the table.

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BS 57:1951

14 © BSI 09-1999

Appendix A Special types of screws not normally stocked

Table 13 — Raised cheese (fillister) head screwsNOTE These screws are not standard. The dimensions are included in this standard solely in order that they may be kept on record. When required, these screws should be ordered to the lengths given in Table 7 (Cheese and countersunk head screws).

Figure 14 — Raised cheese (fillister) head screw1 2 3 4 5 6 7 8 9 10 11 12 13 14

B.A. No.

Diameter of shank and

major diameter of

thread

Diameter of head

Depth of head RadiusRadius under head

slot

Total depth Width Depth

D A B M K F R H J

max. max. min. nom. approx. max. min. nom. max. max. min. nom.

mm. in. in. in. in. in. in. in. in. in. in. in. in.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

6.0

5.3

4.7

4.1

3.6

3.2

2.8

2.5

2.2

1.9

1.7

1.5

1.3

1.2

1.0

0.9

0.79

0.236

0.209

0.185

0.161

0.142

0.126

0.110

0.098

0.087

0.075

0.067

0.059

0.051

0.047

0.039

0.035

0.031

0.413

0.366

0.319

0.283

0.252

0.221

0.194

0.173

0.157

0.128

0.112

0.110

0.095

0.081

0.064

0.064

0.058

0.403

0.356

0.309

0.273

0.242

0.211

0.184

0.163

0.147

0.123

0.107

0.105

0.090

0.076

0.059

0.059

0.054

0.163

0.144

0.126

0.111

0.099

0.086

0.076

0.067

0.061

0.050

0.043

0.043

0.037

0.031

0.025

0.025

0.022

0.048

0.042

0.036

0.035

0.029

0.026

0.023

0.022

0.019

0.014

0.013

0.013

0.012

0.009

0.008

0.008

0.006

0.215

0.189

0.165

0.149

0.131

0.114

0.101

0.091

0.082

0.066

0.058

0.058

0.050

0.041

0.034

0.034

0.029

0.207

0.182

0.158

0.143

0.125

0.109

0.096

0.086

0.078

0.062

0.054

0.054

0.047

0.038

0.031

0.031

0.026

0.472

0.417

0.370

0.323

0.283

0.252

0.220

0.197

0.173

0.150

0.134

0.118

0.102

0.094

0.079

0.071

0.062

0.015

0.015

0.015

0.015

0.010

0.010

0.010

0.010

0.010

0.007

0.007

0.005

0.005

0.005

0.003

0.003

0.003

0.064

0.058

0.052

0.047

0.040

0.040

0.033

0.033

0.030

0.030

0.024

0.024

0.020

0.020

0.015

0.015

0.013

0.056

0.050

0.044

0.039

0.034

0.034

0.027

0.027

0.024

0.024

0.019

0.019

0.015

0.015

0.011

0.011

0.009

0.107

0.094

0.082

0.074

0.065

0.057

0.050

0.045

0.041

0.033

0.029

0.029

0.025

0.020

0.017

0.017

0.014NOTE If the slot is produced by plunge milling, dimension J is measured from the upper surface of the head to the point at which the slot breaks out on the surface of the head.

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BS 57:1951

© BSI 09-1999 15

Table 14 — Connection head screwsNOTE These screws are not standard. The dimensions are included in this standard solely in order that they may be kept on record. When required these screws should be ordered to the lengths given in Table 7 (Cheese and countersunk head screws).

Figure 15 — Connection head screw1 2 3 4 5 6 7 8 9 10 11

B.A. No.

Diameter of shank and major diameter

of threadDiameter of head Depth of head

Radius under head

Slot

Width Depth

D A B R H J

max. max. min. max. min. max. max. min. nom.

mm. in. in. in. in. in. in. in. in. in.

012

345

678

91011

121314

1516

6.05.34.7

4.13.63.2

2.82.52.2

1.91.71.5

1.31.21.0

0.90.79

0.2360.2090.185

0.1610.1420.126

0.1100.0980.087

0.0750.0670.059

0.0510.0470.039

0.0350.031

0.4730.4130.366

0.3190.2830.252

0.2210.1940.173

0.1570.1280.110

0.1100.0950.081

0.0640.064

0.4630.4030.356

0.3090.2730.242

0.2110.1840.163

0.1470.1230.105

0.1050.0900.076

0.0590.059

0.1680.1460.130

0.1130.1000.088

0.0780.0680.061

0.0550.0460.039

0.0390.0330.028

0.0230.023

0.1600.1390.123

0.1070.0940.083

0.0730.0640.057

0.0510.0420.036

0.0360.0300.025

0.0200.020

0.0150.0150.015

0.0150.0100.010

0.0100.0100.010

0.0070.0070.005

0.0050.0050.003

0.0030.003

0.0640.0580.052

0.0470.0400.040

0.0330.0330.030

0.0300.0240.024

0.0200.0200.015

0.0150.013

0.0560.0500.044

0.0390.0340.034

0.0270.0270.024

0.0240.0190.019

0.0150.0150.011

0.0110.009

0.0750.0660.058

0.0510.0450.040

0.0350.0310.027

0.0240.0200.020

0.0170.0140.012

0.0120.010

NOTE If the slot is produced by plunge milling, dimension J is measured from the upper surface of the head to the point at which the slot breaks out on the surface of the head.

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BS 57:1951

16 © BSI 09-1999

Appendix B Approximate proportions

Appendix C Metric slot widths

In order to achieve rationalization of slotting saws and screwdriver blades, it has been agreed that metric slot widths as specified in BS 4183 should be applied to all types of slotted screws. The metric slot widths which will be applicable to the screws in this obsolescent British Standard are shown below.During the remainder of the life of this standard, manufacturers will gradually introduce the metric slot widths and during this period screws with slot widths conforming to the dimensions given in either Table 1, Table 2, Table 3, Table 4, Table 13 and Table 14 or the table below, are deemed acceptable.

Screws

Type of screwDiameter of head

(max.)Depth of head

(max.)

Cheese head screw Based on the rule A = 1.75D; but the dimensions have been adjusted slightly so that they come within the diameters of available round bars to BS limits.

0.7D

Round head screw 0.7D

Countersunk head screw 0.45D

Raised countersunk (instrument) head screw

Countersunk portion= 0.45DTotal depth = 0.65D

Raised cheese (fillister) head screw

Cylindrical portion= 0.7DTotal depth = 0.9D

Connection head screw Based on 2D, but see note above. 0.7D

Hexagonal screw and bolt heads and nuts

Width across flats(max.)

Thickness(max.)

Screws and bolts 1.75D 0.75D

Ordinary (or full) nuts 1.75D 0, 1, and 2 B.A. = 0.9D3 B.A. and smaller = 0.95D

Thin (or lock) nuts 1.75D 2/3D

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BS 57:1951

© BSI 09-1999 17

Table 15 — Slot widths

B.A. No.Slot widths

max. min. max. min.

012

345

678

91011

121314

1516

mm

1.911.511.51

1.201.001.00

0.800.800.70

0.700.60No change

No changeNo changeNo change

No changeNo change

mm

1.661.261.26

1.060.860.86

0.660.660.56

0.560.46No change

No changeNo changeNo change

No changeNo change

in.

0.0750.0600.060

0.0480.0400.040

0.0320.0320.028

0.0280.024No change

No changeNo changeNo change

No changeNo change

in.

0.0650.0500.050

0.0420.0340.034

0.0260.0260.022

0.0220.018No change

No changeNo changeNo change

No changeNo change

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BS 57:1951

BSI389 Chiswick High RoadLondonW4 4AL

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