Unified coarse thread series UNC in to 4 in diameter; Unified fine thread series UNF in to 1 in; Unified extra fine thread series UNEF in to 1 11/16 in. Standard constant pitch series for a graduated system of diameter/pitch combinations. Basic and design forms. Tables of basic dimensions, limits and tolerances for all diameter/pitch combinations in UNC, UNF, UNEF and standard constant pitch series given for the three classes of internal and external threads. Bases of tolerances for Unified screw threads; five sizes below in diameter for attachment purposes and for general use in aircraft appended. Evolved through international discussions between UK, Canada, USA. In accord with corresponding sections of American standard ASA B1.1-1960.

? British Standards Institution 2013

Amendment notes:
AMD 1345 published 15 January 1974
AMD 2782 published 15 March 1979

BS 1580-1:2007