Specifically designed to fit under the stock or aftermarket primary/derby covers and increase the capacity of your stock clutch by using stainless steel weighted arms that progressively increase pressure to the clutch as rpm increases. This also allows lever effort to be kept to a minimum - even with big-inch motors. Three different sets of six coil springs (light, medium, heavy) are included for a variety of spring pressure options. Coil spring design provides much smoother shifting and a more progressive, linear engagement compared to a diaphragm-type spring. Simple bolt-on installation is all that is required with no modifications needed. Made in the U.S.A..