This is a Replacement Gasket Set for the O.S. 32SX-H Helicopter Engine. 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.:19.8mm(0.782") 26.4mm(1.041") O.D.:26.1mm(1.030") 29.6mm(1.166") Thick:0.1mm(0.004") 0.0mm(0.003") MAF11/23/98 ir/jl