Crupi Aluminum Crank Screw Description: The Crupi Alloy Crank Screw is a replacement crank screw for all Rhythm cranks as well as the Crupi Pro Cranks. All nuts, bolts, and screws on your bike require maintenance, that goes double for your cranks. Don't let your cranks come loose while on the track, make sure your bolts are in good shape and pick up a fresh one today if needed. Specifications: Size: 18mm Material: Alloy