2a 1st end thread class 12 1st end thread quantity per inch differentiated free from mercury contanmination; for navy nuclaer propulsion plant un 1st end thread series
3a 1st end thread class 20 1st end thread quantity per inch w/square mtg flange, four 0.144 in. dia mtg holes spaced 1.060 in. c to c unjf 2nd end thread series
Used on 92f support equipment, f-16 aircraft. 2a all ends thread class 12 all ends thread quantity per inch passivate surface treated un all ends thread series