When you don’t know the exact shim thickness you’ll need, keep multiple shim thicknesses for keyed shafts on hand so you always have the right one. Fit these notched shims around keyed shafts and arbors that have a key inserted. Use them on keyed shafts to precisely align and space gears, sprockets, and bearings. On keyed arbors, they’re often used to accurately space saw blades and cutters. These shims are often referred to as arbor spacers.

You can stack multiple shims to achieve your exact thickness, but stacking more than four may cause them to shift. Remember, fewer shims are better, so a couple of thicker shims are more stable than a bunch of thin shims.