Hilliard's Extreme Duty - 3/4" Bore 12 Tooth 35 Chain Hilliard's patent-pending Extreme Duty centrifugal clutch can handle higher temperatures to offer longer clutch life. Stock engagement at 2300 RPM's Bi-Directional, can run clockwise & counter clockwise. Dissipates heat better, extending clutch life. Clutch is easily tuned for your specific need. Quick change spring and sprocket design. No special tools needed. Built-in internal keyway. Must use crankshaft bolt. Hilliard clutches are very sensitive to gearing. You must use at least a 6 to 1 gear ratio with tires at 14" or less in height. No warranty is available for Hilliard clutches because of this!