Ultra Pro Magnum Roller Rocker Arms not only live up to the lofty standards of the original Pro Magnums. The 8650 chromemoly material and arched, web-like design deliver increased strength and rigidity while still reducing the moment of inertia and optimizing the dynamic balance. A unique black oxide exterior finish helps prevent corrosion and increases durability. Featuring Oversized trunnions, precision-sorted needle bearings and hardened Roller tips for the ultimate in performance and dependability. Optimized retainer and valve spring clearances allow for use of most diameter springs, retainers and +.050" locks without clearance or fitment issues.Chrysler 383-440 Big Block - Shaft Mounted - 1.5 Ratio. Investment cast 8650 chromemoly body and arched, web-like design deliver increased strength and rigidity while still reducing the moment of inertia. Unique black oxide exterior finish helps prevent corrosion and increases durability. Optimized retainer and valve spring clearances allow for use of most diameter springs, retainers and +.050" locks without clearance or fitment issues. Feature Oversized trunnions, precision-sorted needle bearings and hardened Roller tips. Lifetime Warranty - So strong that we guarantee the Rocker bodies against breakage for life. For use with up to 850 lbs of open spring pressure. Requires ball/ball style pushrods.