Class 150 threaded stainless steel fittings connect with medium-pressure (300-999 psi) pipe. Threaded pipe fittings are threaded on both connection ends. Female threads are on the inside of a fitting. Male threads are on the outside of a fitting and screw into the female threads. Threaded connections include NPT (National Pipe Thread) or BSPT (British Standard Pipe Taper), and use PTFE tape to secure seal. Type 304 stainless steel, a chromium-nickel material, resists corrosion caused by water, heat, saltwater, acids, minerals, and peaty soils. Type 316 stainless steel has a higher nickel content than 304 stainless, plus molybdenum, for even greater corrosion resistance.