On LS1, LS6 & LS2 engines the crankshaft and factory harmonic balancer does not use a keyway to positively locate and lock the balancer. In high horsepower applications the pulley can spin on the crankshaft sometimes so severely that the crankshaft and balancer can be damaged.
The ATI crankshaft pin drill fixture kit is designed to pin the crankshaft for high-rpm, supercharged, turbocharged, or other high-horsepower engines. They include a billet aluminum black-anodized drill fixture, a hardened 11/64 in. drill bit, an alignment tool, and pins for the crankshaft.