This is a replacement gasket set for the O.S. .61RX-H and .61SX-H helicopter engines. INCLUDES: One metal cylinder head gasket(shim) One fiber backplate gasket SPECS: Head gasket: outside diameter - 32mm(1.26") inside diameter - 24mm(.94") thickness - .23mm(.009") Backplate gasket: outside diameter - 42mm(4.65") inside diameter - 36mm(4.42") btm 04/06/94