John Guest Acetal Copolymer Tube Fitting, Imperial Single Check Valve, 3/8" Tube OD Imperial single check valve to prevent flow reversal in a liquid piping system Accepts nylon and polyurethane tube fittings Made of acetal copolymer plastic for low moisture absorption and high tensile and flexural strength Working pressure of up to 145 psi Meets NSF/ANSI standards 14, 51, and 61 for quality assurance