Custom tooling was created to provide a countersink relief for the bolt/nut head versus machining away the entire end of the shaft per the factory designRecommended for all M-Eight engines and especially for engines running higher lift camshafts and heavier valve spring pressuresOver double the strength of factory rocker shaftsGas nitrated and final surface treatedPrecision ground from 4140HT steelDesigned with strength in mindMade in the USA