Used on special aircraft and engine tool and support equipment/parts (air compressor). navy: washer, aircraft equipment next higher assy is nsn 4310-01-481-7772; compressor unit, reciprocating
Used on los angeles class ssn (688);embt vent chk. 3b thread class right-hand 20 thread quantity per inch four slots equally spaced, 0.093 in. nom. wide, located on the square end