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 1in. A standard con stant 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 a ll 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.