The NSH21-P series is poppet style nipple designed to work with the NSH25-P - coupler. The poppet type checks will interchange with ball type, but they are not designed for use with each other and may affect performance). Compatible with New Line NS20/NS40 series, Parker/Pioneer 4000 series, Safeway S20/40/70 series, Dayco QD2/QD4 series, Snaptite 21 series, Perfecting R series, and Aeroquip FD76 series. They come with Buna-N seals (-40°C (-40°F) to +121°C (+250°F), other seals available on request) and available with NPT, SAE ORB, or BSPP threads.