3a all ends thread class 12 first quick disconnect end thread quantity per inch passivate body surface treated male coupling half un all ends thread series
2a 2nd end thread class 12 1st end thread quantity per inch knurled round nut on swivel end; painted olive drab cadmium surface treated un 1st end thread series
Used on aircraft application. 2a 1st end bulkhead thread class 16 1st end bulkhead thread quantity per inch anodize surface treated flared w/ bulkhead thread un 1st end bulkhead thread series