Milton (S-614-4) 1/4" NPT Brass Compressor Tank Drain Cock -Pack of 2 NPT: 1/4" national pipe thread. USE: To replace old or damaged drain cocks on compressor tanks. DURABLE: Brass body and steel handle. RELEASE: Air from tanks before replacing drain cock. Turn handle to drain water. Close when water is drained. OTHER SIZES OFFERED: Milton also offers drain cocks in 1/2", 1/8", and 3/8" NPT sizes.