Specifies the coarse thread series (designation UNC) from 2 to 4 in. diameter, fine thread series (designation UNF) from 1/4 to 1-1/2 in. and extra fine thread series (designation UNEF) from 1/4 to 1-11/16 in. A standard constant pitch series arranged to give a graduated system of diameter pitch combinations is also included. The basic and design forms of the thread are defined and tables of basic dimensions, limits and tolerances for all the diameter/pitch combinations in the UNC, UNF, UNEF and the standard constant pitch series are given for the three classes of internal and external threads. The bases of tolerances for threads 2 in. and larger are included as an appendix as are details of five sizes below 2 in. diameter for attachment purposes and for general use in the aircraft industry.