The next design evolution of the Hi-Techâ„¢ Stainless Steel Roller Rocker Arms are built to outlast and outperform in accuracy and strength. The Ultra Pro Magnumâ„¢ XD Rocker Arms are engineered from durable 8650 Steel and include a machined billet Pushrod seat insert for a wide range of super accurate ratios. A unique and wide ratio range to fit almost any popular application from 1.5 to 1.73 in .5 increments for Chevy and 1.6 to 1.73 for various Ford Applications is available. These XD Rockers are fully rebuildable and boast precision-sorted needle bearings and hardened Roller tips. And, they work with most diameter springs and retainers. The new XD design utilizes advanced FEA and CAD design and development to improve strength, stiffness and MOI optimization for drag and circle track Applications.Machined billet Pushrod seat insert for wide range of Rocker ratios used in popular Chevy and Ford Applications8650 Steel construction outlasts and outperforms other Rockers in accuracy and strengthPrecision-sorted needle bearings better distribute the load and reduce wear for a longer service lifeEngineered for use in endurance, circle track and drag Race Applications with improved strength and durability