his cap has been designed to be used with our PCO38 Tapping Head for the PET Mini Keg Range, with a specific pressure limit of 35psi / 2.5bar. As it is a standard PET bottle thread (PCO1881) it can also be used on the FermZilla Collection Container / Lid. Please Note: Never exceed the pressure capabilities of your vessel. PRV's are not spunding valves! Check out our blog article explaining this in further detail: Why you should never use a pressure relief valve as a spunding valve.