These new precision machined billet axle blocks utilize a YZ250 axle (P.N.: MX-AXL22-KT - required) allowing the left axle block to float similar to the Japanese design. The Japanese axle which is forged also provides a little more flex that the stock axle which is just a pipe with threads on each end. Advantages are better tire traction and more comfort from the rear of the motorcycle under hard acceleration. Weighs just under the stock system.