This piston will only fit the Ramset Cobra PLUS, with power adjustment. There are two other style cobra pluses. This IS meant for the cobra plus that has a plastic housing and Silencer. ( Newest Style ) It is NOT meant for the cobra plus with the front and rear barrel that connects together with a shear clip ( Oldest Style ) It is also NOT meant for the Cobra Plus that has a buffer and a fastener guide that screws into the barrel. Please refer to your tool manual to verify part 585320.