This is the Propeller Washer for the O.S. Engines GT55 Gasoline Airplane Engine (OSMG1555). FEATURES: Aluminum construction Silver in color INCLUDES: One prop washer - part #13 in engine part list REQUIRES: Installation on crankshaft SPECS: Outer Diameter: 40mm (1.57") Inner Diameter: 10mm (0.39") Thickness: 4mm (0.16") OS EnginesPart OSM29709000