BS 1657:1950

Co-operating organizations
Foreword
Specification
1 Scope
2 Definitions
3 Basic form of British Standard buttress thread
4 Preferred diameters
5 Preferred pitches
6 Tolerances
7 Allowances
8 Designation of British Standard buttress threads
9 Gauges
Tables
1 Numerical data for standard form buttress screw
   threads
2 Tolerances. Close class
3 Tolerances. Medium class
4 Tolerances. Free class
5 Allowances. All classes
   Fig. 2: Relative tolerances and allowances for the
            three classes of buttress threads
   Fig. 3: Disposition of allowances and tolerances for
            standard form buttress screw threads
6 Design sizes for gauges
   Fig. 4: Thread forms of buttress thread gauges
7 Numerical data for special 0 deg/52 deg buttress
   screw threads
8 Thread measuring cylinders for standard form
   buttress threads
9 Thread measuring cylinders for special 0 deg/52 deg
   form buttress threads
Appendices
A Special 0 deg/52 deg form of buttress thread
B Effective diameter equivalents for pitch and angle
   errors
C Measurement of effective diameters of buttress screws

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.

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.