This is a for a 6mm push fit one way valve i.e. None return valve, fitting for 6mm OD tubing. It will only alow air to flow in one direction only, Ideal if you have two compressors working on one air line and want to keep the air going the same way, or want air to stay in one part of a pneumatic system etc etc!! the only limits are your imagination!
It is high quality industrial standard component made by Legris which is one of the leading manufactures of pneumatic components, this component will give you years of trouble free operation. The collar's are colour coded to aid installation, the direction of flow is from the green collar to the red collar i.e air will not flow back through the red collar. There are no specifications of what pressure it will "crack" at, e.g. "flow will start above 10psi", but when I have tested them they all seem to crack around 5psi, apart from the first time which takes a little more pressure.