Specifies requirements for British Association (BA) screw threads in sizes 0 BA (6 mm diameter) to 25 BA (0.25 mm diameter) inclusive. It gives information on the screw thread system, including tolerances, deviations, symbols used for the screw thread parameters, and designation, together with requirements for associated gauges and gauging practices used for the verification of the screw threads for sizes from 0 BA to 10 BA inclusive. Appendices give the basis of the tabulated values, notes on the pitch diameter equivalent of pitch and angle errors, and notes on the verification of screw threads.

This standard specifies requirements for British Association (BA) screw threads in sizes 0 BA (6.00 mm diameter) to 25 BA (0.25 mm diameter) inclusive.The standard gives information on the screw thread system, including tolerances, deviations, symbols used for the screw thread parameters, and designation. Requirements are also specified for associated gauges and gauging practices used for the verification of the screw threads for sizes from 0 BA to 10 BA inclusive. Appendices are included giving the basis of the tabulated values, notes on the pitch diameter equivalent of pitch and angle errors, and notes on the verification of screw threads.NOTES:1. Because the tolerances as calculated from the formulas given in Appendix A require rounding, the values for the various parameters given in the tables are to be taken as authoritative for the application of this standard.2. These screw threads are obsolescent and should not be used in new designs.