These are a high-quality harmonic balancer bolts from GM Performance Parts. These GM Performance Parts harmonic balancer bolts are made of high-quality steel and are heat-treated for extra strength. GM Performance Parts harmonic balancer bolts feature a hex head to prevent socket slippage. The factory LS series engines harmonic balancer bolts are a torque to yield design from the factory. This means you can only use them one time so if you remove the balancer you need to replace the bolt.