The patented Roller Cam Pin is another example of how far POF-USA will go to reduce friction and drag. Standard AR cam pins feature a square head that grinds along the inside of the aluminum receiver. The nickel-plated roller, on POF-USA's cam pin, smoothly rolls along the receiver without gouging the receiver. As a result, you will never worry about cam slot wear again. Notes: The AR-15 version is made for use with Piston AR-15 bolt carrier groups. If you wish to upgrade a Mil-spec direct impingement AR-15 bolt carrier, you will need the Gas Key Upgrade Kit.The AR-15 version fits with all Gas Piston bolt carriers, all Revolution bolt carriers, and all Rogue bolt carriers.