JR ALUMINUM SHAFT STOPPER DESCRIPTION This set includes 4 shaft stoppers for use on Mini 4WD machine axles, enabling you to attach your wheels to 72mm hex shafts with precision. They are made from lightweight and durable aluminum. Aluminum Shaft Stopper x4 2x4mm Screws for attachment x5 For use with all Mini 4WD and Mini 4WD cars (except Super X and Super XX cars) fitted with 72mm hex shafts. Note: Some bodies may require modification.