COMP Cams 862-12 Pro Magnum Hydraulic Lifter for 289-302 Small Block/351 Windsor/Cleveland/429-460 Ford, (Set of 12) 0.875 inches diameter; 105 gram weight; 1.95 inches seat height Specifically designed to perform at higher engine speeds with significant power increase over standard hydraulic lifters Proper position of internal piston at higher rpm prevents lifters form harmful pumping up Adjustable valve train required Pre-load lifters 0.002 inches - 0.004 inches with engine warm