Link Bar Retro-Fit Hydraulic Roller Lifters (Patent Pending). Precise piston fit for lowest leakdown rate. Patent-pending piston allows trapped air to escape lifter for faster "pump up". Axles produced from premium 52100 heat-treated Steel for increased wear resistance and overall strength. Lightweight body design. Includes (12) lifters. Applications: Buick 231 V6 (Requiring shrouded wheel)