Twin Power Extra Plate Clutch Kit For Harley Big Twin Features The kit for high performance applications Includes 10 friction plates with race proven friction material on 6061 T6 aluminum cores 9 tempered steel drive plates and a 10 stronger than stock diaphragm spring Pre-measured stack height for easy, accurate installation 11 more surface area than stock Made in the USA Note: For use with petroleum based, non-synthetic, light viscosity primary oil.