Unified coarse thread series UNC 3/16 in to 4 in diameter; Unified fine thread series UNF 3/16 in to 1½ in; Unified extra fine thread series UNEF 3/16 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 3/16 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.Cross References:BS 84BS 93BS 768BS 919:Part 1 BS 1750BS 1768BS 1769BS 1981BS 2470BS 2708BS 3139BS 3382BS 3580BS 4084Incorporates the following:AMD 1345 published 15 January 1974AMD 2782 published 15 March 1979