Tool Steel Ford 221-302, 351W, 351C, 351M, 400, 429-460 Mech Flat Tappet 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.