MIL-S-8879C, MILITARY SPECIFICATION: SCREW THREADS, CONTROLLED RADIUS ROOT WITH INCREASED MINOR DIAMETER, GENERAL SPECIFICATION FOR (25 JUL 1991) [S/S BY SAE-AS8879]., This specification is the specification identified in FED-STD-H28/4 and contains the detailed requirements for use in acquisition of threaded products with controlled root radius screw threads, UNJ symbol.