BS 93:2008

$142.49

British Association (B.A.) screw threads. Requirements

Published By	Publication Date	Number of Pages
BSI	2008	26

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Categories: 21.040.30 - Special screw threads, BSI

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Description

This British Standard specifies limits of sizes, and tolerances, for single start parallel screw threads of British Association (B.A.) form. It is not applicable to screw threads associated with interference fits, such as those on the “metal ends” of studs and in the corresponding tapped holes.

This British Standard specifies the following:

basic sizes for B.A. threads, sizes 0 B.A. to 16 B.A.;
limits of size, and tolerances, for close class and normal class external threads of sizes 0 B.A. to 10 B.A.;
limits of size, and tolerances, for normal class external threads of sizes 11 B.A. to 16 B.A.;
limits of size, and tolerances, for a single class of internal threads of sizes 0 B.A. to 16 B.A.

PDF Catalog

PDF Pages	PDF Title
3	Contents 1 Scope 1 2 Normative references 1 3 Terms and definitions and symbols 1 4 Profile of British Association (B.A.) screw thread 2 5 Basic sizes of B.A. threads 3 6 Tolerance classes and limits of sizes, and tolerances, for B.A. threads 3 7 Gauges 4 Annexes Annex A (informative) Basis of sizes of B.A. threads 12 Annex B (informative) Bases of allowances and tolerances for B.A. threads 12 Annex C (informative) Effect of errors in pitch and flank angle on the effective diameter 14 Annex D (informative) Approximate inch equivalents of B.A. thread sizes 16 Bibliography 21 List of figures Figure 1 – Basic form of B.A. thread 2 Figure 2 – Tolerance zones for a close class external thread and an internal thread 5 Figure 3 – Tolerance zones for a normal class external thread and an internal thread 5 Figure 4 – Example of effective diameter tolerance zones (Effective diameter tolerance zones for size 2 B.A. threads illustrated) 6 List of tables Table 1 – Basic sizes of British Association (B.A.) screw threads 7 Table 2 – Limits and tolerances for close class external threads – Sizes 0 B.A. to 10 B.A. 8 Table 3 – Limits and tolerances for normal class external threads – Sizes 0 B.A. to 10 B.A. 9 Table 4 – Limits and tolerances for normal class external threads – Sizes 11 B.A. to 16 B.A. 10 Table 5 – Limits and tolerances for internal threads – Sizes 0 B.A. to 16 B.A. 11 Table B.1 – Summary of tolerance formulae 13 Table D.1 – Basic sizes of British Association (B.A.) screw threads – Approximate inch equivalents 16 Table D.2 – Limits and tolerances for close class external threads – Sizes 0 B.A. to 10 B.A. – Approximate inch equivalents 17 Table D.3 – Limits and tolerances for normal class external threads – Sizes 0 B.A. to 10 B.A. – Approximate inch equivalents 18 Table D.4 – Limits and tolerances for normal class external threads – Sizes 11 B.A. to 16 B.A. – Approximate inch equivalents 19 Table D.5 – Limits and tolerances for internal threads – Sizes 0 B.A. to 16 B.A. – Approximate inch equivalents 20
4	Foreword
5	1 Scope a) basic sizes for B.A. threads, sizes 0 B.A. to 16 B.A.; b) limits of size, and tolerances, for close class and normal class external threads of sizes 0 B.A. to 10 B.A.; c) limits of size, and tolerances, for normal class external threads of sizes 11 B.A. to 16 B.A.; d) limits of size, and tolerances, for a single class of internal threads of sizes 0 B.A. to 16 B.A. 2 Normative references 3 Terms and definitions and symbols 3.1 Terms and definitions
6	3.2 Symbols 4 Profile of British Association (B.A.) screw thread Figure 1 Basic form of B.A. thread
7	5 Basic sizes of B.A. threads 6 Tolerance classes and limits of sizes, and tolerances, for B.A. threads a) Close class external threads. Limits and tolerances for close class external threads of sizes 0 B.A. to 10 B.A. shall be as specified in Table 2. b) Normal class external threads. Limits and tolerances for normal class external threads of sizes 0 B.A. to 10 B.A. shall be as…
8	7 Gauges
9	Figure 2 Tolerance zones for a close class external thread and an internal thread Figure 3 Tolerance zones for a normal class external thread and an internal thread
10	Figure 4 Example of effective diameter tolerance zones (Effective diameter tolerance zones for size 2 B.A. threads illustrated)
11	Table 1 Basic sizes of British Association (B.A.) screw threads
12	Table 2 Limits and tolerances for close class external threads – Sizes 0 B.A. to 10 B.A.
13	Table 3 Limits and tolerances for normal class external threads – Sizes 0 B.A. to 10 B.A.
14	Table 4 Limits and tolerances for normal class external threads – Sizes 11 B.A. to 16 B.A.
15	Table 5 Limits and tolerances for internal threads – Sizes 0 B.A. to 16 B.A.
16	Annex A (informative) Basis of sizes of B.A. threads Annex B (informative) Bases of allowances and tolerances for B.A. threads B.1 Allowances B.2 Tolerances B.3 Tolerances on effective diameters B.3.1 External threads
17	B.3.2 Internal threads B.4 Tolerances on major diameters B.4.1 External threads B.4.2 Internal threads B.5 Tolerances on minor diameters B.5.1 External threads B.5.2 Internal threads Table B.1 Summary of tolerance formulae
18	Annex C (informative) Effect of errors in pitch and flank angle on the effective diameter C.1 Effect of pitch errors C.2 Effect of errors in flank angle C.3 Criteria for acceptability of a combination of errors in the effective diameter, pitch and flank angle of a screw thread a) External threads. To be acceptable, the simple effective diameter of an external thread (as measured along the pitch line of … b) Internal threads. To be acceptable, the simple effective diameter of an internal thread (as measured along the pitch line of …
20	Annex D (informative) Approximate inch equivalents of B.A. thread sizes Table D.1 Basic sizes of British Association (B.A.) screw threads – Approximate inch equivalents
21	Table D.2 Limits and tolerances for close class external threads – Sizes 0 B.A. to 10 B.A. – Approximate inch equivalents
22	Table D.3 Limits and tolerances for normal class external threads – Sizes 0 B.A. to 10 B.A. – Approximate inch equivalents
23	Table D.4 Limits and tolerances for normal class external threads – Sizes 11 B.A. to 16 B.A. – Approximate inch equivalents
24	Table D.5 Limits and tolerances for internal threads – Sizes 0 B.A. to 16 B.A. – Approximate inch equivalents
25	Bibliography

Additional information

Status	Confirmed
Pages	26
Publication Date	2008-09-30
ISBN	978 0 580 60893 3
Standard Number	BS 93:2008
Title	British Association (B.A.) screw threads. Requirements
Replaces	BS 93:1951
Descriptors	Dimensional tolerances, Normal threads, Bolts, Designations, Nuts, Threaded fasteners, Dimensions, Metal coatings, Thread pitch, Thread forms, Diameter, British Association screw threads, Close-fit threads, Threads, Parallel threads, Fits
Publisher	BSI
Committee	FME/9
ICS Codes	21.040.30 - Special screw threads

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