This listing is for one stainless steel Check Valve. Both ends are threaded 1/4" male NPT.  The body is stainless, the ball is stainless, the O-ring is Teflon, the spring is stainless, the O-ring retainer is stainless, and the jam screw is steel. I have tested this check valve to 10,000PSI. It is probably good for more than that, but that was the highest my gauge would read. I have conservatively rated it at 5000psi.  For your average scuba or paintball compressor (3000 to 5000psi), this check will work awesome. It will work good for almost any gas or liquid. The hole through is about .125" so this check is good for high pressure, but not for very high flowrates. I do not suggest using this check valve on any system that requires more than about 20CFM.  Anything less than that, and it will be fine.  If you have any questions, just ask.