BS 1157:1975

This standard BS 1157:1975 Recommendations for tapping drill sizes for use with fluted taps is classified in these ICS categories:

• 25.100.30 Drills, countersinks, reamers

These recommendations give drill sizes, covered by BS 328-1, for use prior to tapping the threads indicated. Table 1 to Table 14 cover preferred thread forms and Table 15 to Table 17 cover non-preferred forms. Appendix A covers alternative tapping drill sizes.

Sizes for ISO internal metric threads to BS 3643 (Parts 1, 2 and 3) and for internal threads to BS 21, 84, 93, 1580 (Parts 1, 2 and 3) and 2779. Alternative sizes in appendix.