Centrifugal Clutch 10 tooth, 3/4" bore, used with #41/420/40 chain. Clutch comes with 3/16" key and two set screws. Quality aftermarket centrifugal clutch. 10T sprocket for #41/420/40 chain3/4" center bore with 3/16" key way NO WARRANTY ON CLUTCHES. OIL CLUTCH EVERY HOUR