SMC Male Straight fittings are male NPT on one side, and PTC on the other. SMC fittings feature a metal sleeve which aligns with the inside of the air line, providing an improved seal for 1/4, 3/8 and 1/2 PTC options. SMC fittings are DOT approved for 1/4, 3/8 and 1/2 inch PTC options.