Features & Benefits of T&D shaft-mount roller rocker systems T&D rocker arms have an oil passage (see diagram) built into most rocker arms to channel pressurized oil from the pushrod cup to the shaft bearings and then on to the roller tip. T&D's 7/16” adjuster screw and heat-treated alloy steel jam nut are the largest in the industry, giving more thread contact area to positively secure lash settings. Each adjuster is broached for a big 3/16" socket to eliminate twisted hex keys. T&D’s larger diameter shafts are made from 4130 steel, deep case hardened and tempered for maximum wear resistance and strength. T&D aluminum rocker bodies use 2024 aluminum made to our specifications for improved tensile and yield strength, and increased notch sensitivity, fatigue resistance, strength at elevated temperatures and chemical resistance. T&D has gone to great lengths to find the right material to use in its steel rocker bodies, which remains proprietary. Extensive R&D, and constant hands-on usage, has given T&D a distinct advantage in the area of steel rocker development. Presently, many of the steel rockers are within a few grams of the aluminum ones they replace. Every T&D rocker system is designed with racers and ease of installation and maintenance in mind. Most applications require no head modifications, no machining of any kind. If machining is required, full instructions are included. All hardware and shims necessary to attach a rocker system are included. On models with individual shafts, individual rockers can be removed quickly for valve spring service. Most T&D rocker systems are rebuildable. T&D tests every rocker arm against the competition for weight, mass moment of inertia, deflection, hardness and cycle durability. Through this testing, T&D rockers have been continuously improved to be the lightest, most efficient, and most durable rocker arms on the market. Through rigorous on-track testing, T&D rocker arms have survived the torture tests, in all forms of racing.