Used on close in weapon system ciws-phalanx. 3a 1st end thread class 20 1st end thread quantity per inch passivate surface treated screwed un 1st end thread series
Used on skid mounted. 3a 1st end bulkhead thread class 12 1st end bulkhead thread quantity per inch k denotes corrosion resistant steel, type 316 passivate surface treated threaded unj 1st end bulkhead thread series