These gems are machined to precisely fit the preload adjuster cap on all modern 24mm spindle Shimano cranks. The finger spline offers good leverage to install, remove, or adjust the preload cap. We also added a 5mm hex in the center should you need a little extra leverage that a hex key provides. These are also compatible with our fit kits and with the addition of a saddle height bullet can be used to more accurately measure saddle height.