The stock bolts are grade 8.8 and are prone to breaking off in the cylinder head. This causes a lot of noise, possibly engine damage, and sometimes a new cylinder head. This kit replaces the weak factory bolts on the main timing chain guides. Included are . We offer two styles of bolt. The first is a grade 12.9 bolt, they have an allen key head and have a minimum strength of 174,000 psi. We also offer ARP bolts, they take a regular hex socket and are rated at 170,000-180,000 psi.