This is a replacement part for the O.S. FS-40 Surpass four-stroke engine. / / This Package Includes: / (1) Head gasket - this is the thin metal gasket that seals the gap between / the crankcase and cylinder head and also sets the head gap. / / Specifications: / Inner Diameter: 21mm (.827") / Outer Diameter: 26.5mm (1.04") / Thickness: .210mm (.00825") / / JBN 4.4.94 *8)