Specifications: Bore diameter: 0.625 inches (slightly smaller than a Dime Fits: Centrifugal Clutch 11 tooth, 5/8" bore, use 35# chain Predator 2.8 HP 97cc engine, some older 3hp engines Engines with 5/8 inch (0.625 inch) output shaft with standard keyway Set Screws NOT Included. Mounts onto crankshaft using bolt and washer on the end of the crankshaft.