For use with real muscle motors, Zodiac offers you this ultra high performance diaphragm clutch spring. Please note, we do not recommend this spring for street use to it's increased hand-effort requirements and maximized clutch pack pressure. We recommend it "for competition only" applications. If you are making lots of horsepower, this is the spring for you. Will fit Big Twin 1990-1997, Sportster and Buell 1991 to present.