Suitable for M or D type couplers, interchangeable/compatible with most manufacturers. Industrial Type D 1/4-Inch NPT. 4 Ball. High quality brass durable, no rust, more wear resistant than aluminum. With thread sealing tape (Teflon tape), the best sealing and high efficiency. Common Use to air fitting kit for air tools, air compressor, air nailer, air blow gun, pressure washer, air hose.