SPG 3/8-5/16 is Pneuflex' model number of stainless steel union straight reducer push-in fittings of different diameter of connectors. 3/8 x 5/16 inch stainless steel union straight reducer pneumatic fittings is composed of stainless steel body and FKM ( Viton ) seal, which can hold nylon tubing, PU tubing, PE tubing, Teflon tubing and can transfer air, water, oil, weak corrosive fluids.