This is the Front Bearing for the OS 61FX Engines. FEATURES: Steel construction Shielded front (to prevent fuel leakage) Open back (to allow oil in fuel to lubricate balls) INCLUDES: One Ball Bearing REQUIRES: Installation into crankcase SPECS: Inner Diameter: 12mm Outer Diameter: 24mm Thickness: 5.5mm COMMENTS: This is the bearing that sits in the back portion of the crankcase which supports the crankshaft.OS EnginesPart OSM27731000