Designed to securely hold 5/16" TO 9/16" axles for easy wheel hub and pedal adjustments, the AV-4 is a must for every mechanics workbench. Just insert axle into one of the three precision-machined openings and tighten in a bench vise. The AV-4s bridge spring keeps the jaws aligned and allows the tool to automatically open when the bench vise is opened. Aluminum jaws will not damage axle threads.