Sigma slipper clutches are designed to allow easier downshifting on the road or track. Originally a pure race accessory our slipper clutches smooth gear changes for skilled riders and beginners alike by automatically and seamlessly disengaging the clutch whenever engine braking or rear wheel hop becomes an issue. Each clutch is individually designed using carefully chosen ramp angles with ball bearings for the smoothest performance possible. All are supplied with full instructions. Most models use standard springs and plates.