SAE AS8879D

This SAE Aerospace Standard (AS) specifies the characteristics of screw threads – UNJ profile inch series, including a mandatory controlled radius as specified in Table 1 at the root of the external thread. The minor diameter of both external and internal threads provides a basic thread height of .5625H to accommodate the external thread maximum root radius. The following detailed design requirements are included: a. Screw threads – UNJ basic profile and design profiles. b. Standard series of diameter-pitch combinations for nominal thread diameters from 0.060 to 6.000 inches. c. Standard thread classes and form tolerances. d. Formulae for thread dimensions and tolerances. e. Method of designating UNJ threads. f. Tables for selected diameter-pitch combinations for close tolerance mechanical thread applications. g. Tables for screw thread – UNJ profile thread limit dimensions.

This document specifies the geometric design for each characteristic of screw threads – UNJ profile inch series and the conformance requirements. In addition, the purpose of this standard is to: a. Define the geometric requirements for a selected series of Unified Screw Threads, modified to provide a radius at the external thread root. b. Establish requirements for a continuous radius at the root of the external threads. c. Establish requirements for an increase in the minor diameter of both internal and external threads to accommodate the external thread root radius.