Copper Pigtail POL x 1/4″ Inverted Flare – these pigtails connect the regulator to the tank. They are “full flow”, unrestricted. Inlet size is Male POL (CGA-510), the left handed thread that is on 100 lb tanks and the inside threads on OPD valves. The POL nut has a swivel. The outlet is 1/4″ inverted flare. When used with a regulator that has a 1/4″ FNPT inlet, an inverted flare adapter is required.