The hex head cap screw attaches to the engine pulley. This is a genuine part sourced directly from the manufacturer for use in lawn tractors and log splitters made by Ryobi, MTD, Yard Machines, Troy-Bilt, Bolens, and Yard Man. This item is sold individually and is made of metal. A wrench will be necessary during the installation of this part. It will need to be replaced if it strips or breaks.