This is the Replacement Flexible Shaft for the OS Max 21-XM Marine engine. This is the shaft that connects the crankshaft to the outboard propeller. FEATURES: Steel construction Flexible wire INCLUDES: One Flex Shaft REQUIRES: Nothing. This is a direct replacement part. SPECS: Length: 130mm (5.12") Diameter: 3.7mm (0.15") COMMENTS: For the flex shaft tube, use OSMG5864. OS EnginesPart OSM23873000