Retro-Fit High Endurance Vertical Bar Chev Mark IV, Gen 5/6 Hyd Roller Lifters Made for all high endurance performance applications including marine. Proprietary hydraulic valving specifically designed for continuous operation to 6600 rpm. With ideal seat pressures between 140-180 lbs. The lifter body is fully machined from alloy steel bar stock and completely micro polished. The nose wheel is machined from 8620 material and case hardened for durability. Made in the USA!