2807 Series Stainless Steel Shim (12mm ID x 15mm OD, 0.25mm Thickness) - 12 Pack

These 0.25mm thick stainless shims are intended to provide a small amount of necessary space between a 12mm bearing, and the next component in your assembly.  Since the inner race and outer race of most bearings share the same thickness, there’s potential for an item that extends over the outer race to scrape as it rotates.  By adding a shim, that part can rest against the shim and rotate freely without contacting the outer race.