Pro Magnum Hydraulic Flat Tappet Lifters. Specifications .904" Diameter - 107g Weight - 1.84" Seat Height. Specifically designed to perform at higher engine speeds. Proper position of internal piston at higher RPM prevents lifters from harmful "pumping up". Unique design yields significant power increase over standard hydraulic lifters. Adjustable valve train requiredPre-load .002"-.004" with engine warm. Applications: AMC V8 290-401, Chrysler, Small Block V8 273-360Big Block B Series 383-440 ('68+)