These acrylic, block style flow meters are clear and one piece, with built-in, brass, flow-regulating valves suitable for air or oxygen. The scale reads in cubic feet per hour at standard pressure (sea level) and temperature (68°F, 20°C). Connections are 1/8” FNPT. Includes 1/4” inlet/outlet barb brass fittings. Calibrated at 0 psi. One-year warranty.