This is a Replacement Gasket Set for the OS Max .46 FX Engines. INCLUDES: One Head gasket - this very thin metal gasket seals the gap between the cylinder head and the crankcase. One Backplate gasket - this thin paper gasket seals the gap between the backplate and the crankcase. SPECS: Head Gasket: B.P.gasket: I.D.:22.2(0.874") 30.4mm(1.200") O.D.:28.5(1.124") 33.8mm(1.334") Thick: 0.1(0.005") 0.0mm(0.002")OS EnginesPart OSM25614010