This is the replacement Piston for the O.S. .37 SZ-H helicopter engine. FEATURES: Aluminum construction Replaces worn or damaged pistons INCLUDES: One piston REQUIRES: Other related parts include: Piston Ring - OSMG7789 Piston Pin - OSMG7667 Connecting Rod - OSMG3929 SPECS: Height: 19mm (.75") Diameter: .81" (20.55mm) OS EnginesPart OSM23413200