BS.1768 UNIFIED HEXAGON HEAD BOLT & SCREW Dimensions
a) General. The screw threads on bolts, screws and nuts up to and including 1″ Nominal size shall be Unified coarse (UNC) or Unified fine (UNF) in accordance with BS.1580. ‘Unified Screw Threads’ as specified by the purchaser. The screw threads on bolts, screws and nuts in nominal sizes above 1″ shall be Unified coarse (UNC) in accordance with BS.1580. If a finer thread is required, it is recommended that the 8-Thread series shall be used.
b). Bolts and Screws. The Screw threads may be either cut or rolled at the option of the manufacturer and shall conform to the limits and tolerances for Class 2A specified in BS.1580.
c). Nuts. The Screw threads shall conform to the limits and tolerances for Class 2B specified in BS.1580
d). Gauging of Screw Threads. Screw threads shall be gauged in accordance with the system recommended in BS.919, part 1, ‘Gauges for shrew threads of Unified form’. The NOT GO effective diameter screw plug gauge used for checking nuts shall be the low addendum form specified in that standard
*Information is given as guidance only