- Fitting is interchangeable with black cast-iron or steel. - For low-pressure plumbing applications including air, water, natural gas, and steam. Specific Fitting Shape / Square Head Plug Nominal Pipe Size / 1 in Pipe Fitting Material / Malleable Iron Class / 150 Fitting Connection Type / Male NPT Temp. Range / -20 Degrees to 366 Degrees F Plug Construction / Cored Standards / ASME B16.14, ASTM A197, FM Approved, UL Listed