Tool Steel Buick / Cadillac / Chevrolet / Oldsmobile / Pontiac Mech Lifters Intended for use on cast iron camshafts. Ideal for engines turning in excess of 7,000 rpm with higher valve spring pressures. Super fine surface finish of 1-2Ra and built from tool steel for durability and hardness (63-64RC). Lightweight (68+ grams) and are available with an optional “Direct Lube” EDM oil hole (.016in). Compatible with all OE and aftermarket engine blocks. Made in the USA! Note: Required for flat tappet applications in Dart SHP blocks.