Converts stock diaphragm spring to coil spring Increase tunability of clutch More positive linear clutch action Stock clutch center hub must be upgraded to a steel hub This product can be used with Model Part# Harley-Davidson Big Twin H-D# 37550-84A 98-06 CCHD-1 Harley-Davidson Big Twin H-D# 37550-84A 84-89 CCHD-2