MIL-S-45909C, MILITARY SPECIFICATION, STUD, LOCKED IN, RING LOCKED, SERRATED, GENERAL SPECIFICATION FOR (27 MAR 1989) [S/S BY NASM45909]., This specification covers the requirements for locked-in studs. The method of locking the stud is by means of a serrated collar and an accessory lock ring with matching serrations installed within a parent material to prevent rotation.