3b all ends thread class 12 all ends thread quantity per inch will operate at minus 20 deg f cadmium surface treated single joint, elbow design un all ends thread series
3a 2nd end thread class 1st end bukhead thd size 0.750 in. nom, cl 3a, unjf anodize surface treated double joint, double elbow design unjf 2nd end thread series
Used on support equipment,f-16 aircraft. 3a 1st end thread class with bleed hole, with integral cres filter screen, 700 by 80 mesh; weapon system essential passivate surface treated single joint, straight design unf 2nd end thread series