BS 1657:1950

This British Standard relates to screw threads of buttress form and provides:

1. a standard form of thread
2. tables of preferred diameters and of preferred pitches
3. a formula for calculating effective diameter tolerances
4. tolerances for major and minor diameters
5. a system of allowances between mating threads
6. recommended methods of gauging
7. Appendix A giving a special form of buttress thread having a vertical pressure flank
8. Appendix B giving notes on the effective diameter equivalents of pitch and angle errors
9. Appendix C giving notes on the measurement of the effective diameters of buttress threads.

Included angle between pressure and trailing flanks of 52°; standard form of thread has a pressure flank angle of 7°; ‘special’ form has pressure flank normal to axis of screw. No rigid pitch/diameter relationship. Includes preferred series for diameters and pitches. Tables of tolerances and allowance for three classes of fit. System of gauging with notes on appropriate types and sizes of gauge. Method of measurement of effective diameter of buttress threads, tables of dimensions for the sizes of thread measuring cylinders.