This official Campagnolo part is a so-called wave washer that is used when installing Ultra-Torque, Power-Torque, or Over-Torque cranksets with the proper bottom bracket. A wave washer compresses when the crank arm pushes into the bottom bracket cup and is fastened to torque. It provides a bearing preload, protecting from over compressing the bearing into the cup, allowing the bearings to spin freely.

For example, with Ultra-Torque the washer is used on the left side. UT crank arms have the bearing pressed onto the attached axle spindle (unlike systems that have the bearings in the cup already). The wave washer slides over the spindle, to the bearing, then the arm is inserted and mated to the other half of the split spindle system used with a center fitment called a Hirth coupling. A bolt is then inserted into the hollow left arm and fastened to at the Hirth coupling to the drive side arm/spindle section. When fastened to proper torque, the wave washer protects the bearing as stated above with proper preload. This inexpensive but required crucial small part helps ensure the proper function and long life of your UT bearings.