This is a package of 2 brand new exhaust/muffler gaskets that will fit the OS .21 RG , 2 stroke motor as well as many other similar size motors. The exhaust opening matches the engine exhaust. They are slightly thicker and larger than a normal muffler gasket for much longer life and to avoid tearing. Some new engines don't even come with them. Made of high temperature 1/32" automotive grade material to last a long time and avoid any leaking.