Steel. For OEM 30-46 drive ratio. Over tension is an issue with the OEM primary chain tensioner. Unnecessary stresses on chain, sprockets and bearings can cause premature failure. This steel 'Bump Stop' blocks the OEM automatic chain ratcheting system, thus preventing it from ratcheting too far. Adjustments are made by grinding material away from the bump stop's grooved wear marks. Primary chain adjustments can be made together with every 5000 mile primary oil change. Incl. Installation instructions. Permanent modifications are not required.