Bolt MC Chain Adjuster Blocks 2 Pack Black for Yamaha WR250F WR450F YZ125 YZ250 Billet aluminum chain adjuster blocks hold the wheel precisely in place while tightening the chain and stay in position even when the axle is removed Designed to work with only one 12mm (13mm on the KTM) wrench is needed to make chain adjustments Each andonized 6061 aluminum block has laser etched aligning marks and has anti-seixe pre-applied to threads Kawasaki chain adjuster blocks include a 22 mm metal locknut to replace the stock cotter pin and castle nut