This is the Powerglide with a failsafe solid bronze alloy bushing instead of a regular roller bearing. No other differences excist between the regular Powerglide and the Powerglide Steady Roll tappets. Full bearing contact provides more stability; longer life and quieter operation due to the tighter tolerances this bushing design allows. The major drawback of a worn needle bearing roller is they will eventually break; spilling steel needles throughout your engine. This is no longer an issue. Even when the Steady Roll bronze bushing wears out the design is failsafe. Like the other Jims Powerglide™ tappets this Steady Roll version will give you a superior hydraulic function when compared with OEM style equipment; a billet steel body with hand-honed hydraulic unit cavity and an oil fed axle. To get full power; you must have zero valve lash and eliminate collapsing of the hydraulic unit as is found in the OEM unit; also called ''the shock absorber syndrome''. Failing to keep the valve open the full amount results in power loss. The Jims Powerglide tappets come as close to a solid tappet as possible; but are still able to compensate for heat expansion. They will even work well with solid style camshafts. Fits as an oversized upgraded replacement for OEM 18538-99C Standard and 17900022A High Capacity. Note: Standard O.D. is .8420"