*** IN STOCK SHIPS TODAY *** This clamp provides superior strength over the stainless band clamp and is a must for the racer looking to guarantee accurate timing and a stable magneto. Uses a 5/16-18 bolt.Will work with Mallory, FIE or MSD magnetos. Width at the bottom of the groove on the clamp is .560" if you are measuring across the clamping surface of your magneto and magneto drive.