Bolts, Screws, and Nuts BRITISH FASTENERS Machinery's Handbook, 31st Edition
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British Standard Square and Hexagon Bolts, Screws and Nuts.— Important dimensions of precision hexagon bolts, screws and nuts (BSW and BSF threads) as covered by British Standard 1083:1965 are given in Table 1 and Table 2. The use of fasteners in this standard will decrease as fasteners having Unified inch and ISO metric threads come into increas - ing use. Dimensions of Unified precision hexagon bolts, screws and nuts (UNC and UNF threads) are given in BS 1768:1963 (obsolescent); of Unified black hexagon bolts, screws and nuts (UNC and UNF threads) in BS 1769:1951 (obsolescent); and of Unified black square and hexagon bolts, screws and nuts (UNC and UNF threads) in BS 2708:1956 (withdrawn). Unified nominal and basic dimensions in these British Standards are the same as the comparable dimensions in the American Standards, but the tolerances applied to these basic dimensions may differ because of rounding-off practices and other factors. For Unified dimensions of square and hexagon bolts and nuts as given in ANSI/ ASME B18.2.1-2012 and ANSI/ASME B18.2.2-2015 see Table 1 through Table 4 starting on page 1672, and Table 7 to Table 10 starting on page 1677. ISO metric precision hexagon bolts, screws and nuts are specified in the British Standard BS 3692:1967 (obsolescent) (see British Standard ISO Metric Precision Hexagon Bolts, Screws and Nuts starting on page 1766 ), and ISO metric black hexagon bolts, screws and nuts are covered by British Standard BS 4190:1967 (obsolescent). See the section MACHINE SCREWS AND NUTS starting on page 1775 for information on British Standard metric, Unified, Whitworth, and BSF machine screws and nuts. British Standard Screwed Studs.— General purpose screwed studs are covered in British Standard 2693: Part 1:1956. The aim in this standard is to provide for a stud having tol erances which would not render it expensive to manufacture and which could be used in association with standard tapped holes for most purposes. Provision has been made for the use of both Unified Fine threads, Unified Coarse threads, British Standard Fine threads, and British Standard Whitworth threads as shown in the table on page 1761. Designations: The metal end of the stud is the end which is screwed into the component. The nut end is the end of the screw of the stud which is not screwed into the component. The plain portion of the stud is the unthreaded length. Recommended Fitting Practices for Metal End of Stud: It is recommended that holes tapped to Class 3B limits (see Table 3, page 1951 ) in accordance with BS 1580 “Unified Screw Threads” or to Close Class limits in accordance with BS 84 “Screw Threads of Whitworth Form” as appropriate, be used in association with the metal end of the stud specified in this standard. Where fits are not critical, however, holes may be tapped to Class 2B limits (see table on page 1951 ) in accordance with BS 1580 or Normal Class limits in accordance with BS 84. It is recommended that the B.A. stud specified in this standard be associated with holes tapped to the limits specified for nuts in BS 93, 1919 edition. Where fits for these studs are not critical, holes may be tapped to limits specified for nuts in the current edition of BS 93. In general, it will be found that the amount of oversize specified for the studs will produce a satisfactory fit in conjunction with the standard tapping as above. Even when interfer ence is not present, locking will take place on the thread runout which has been carefully controlled for this purpose. Where it is considered essential to assure a true interference fit, higher grade studs should be used. It is recommended that standard studs be used even under special conditions where selective assembly may be necessary.
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