BS 3643-2:1981

This British Standard, a part of the BS 3643 series, specifies the fundamental deviations, tolerances and limits of size for the tolerance classes 4H, 5H, 6H and 7H for internal threads (nuts) and 4h, 6g and 8g for external threads (bolts) where appropriate for:

• coarse pitch series within the range 1 mm to 68 mm diameter
• fine pitch series within the range 1 mm to 33 mm diameter
• constant pitch series within the range 8 mm to 300 mm diameter.

For certain diameter/pitch combinations tolerance class 4H for internal threads and tolerance classes 6h and 4g for external threads have been included in appendix A primarily for aerospace use.