10 Tooth Clutch, 1" Bore CENTRIFUGAL CLUTCH for 40, 41 and 420 chain. For 3 to 7hp engines and rear wheels 15" or shorter. Require a crankshaft with a 1/4" keyway and tapped end so you can screw a bolt into the end of the crankshaft to hold the clutch on. Made in China.