This new 1/2" Rocker Stud and Trunnion Retro-Fit Kit greatly increases the stiffness and stability of any SBC or BBC Ultra Pro Magnumâ„¢ or Ultra Pro Magnumâ„¢ XD Rocker valve train far beyond that of a 7/16" Stud.The COMP Cams 1/2" Rocker Stud and Trunnion Retro-Fit Kit provides a stiffer valve train to achieve maximum valve motion in SBC or BBC engine Applications utilizing Ultra Pro Magnumâ„¢ or Ultra Pro Magnumâ„¢ XD Rocker Arms. It is good for anyone looking for more stiffness with Stud mount Rockers. The kit was originally designed for Applications competing in the NHRA Stock Eliminator class, but it is a great choice for anyone whose sanctioning body's rules do not allow Stud girdles. Featuring 1/2" ARP Studs 1/2" replacement trunnions, 1/2" replacement polylocks, new replacement bearings and new replacement snap rings, the kit includes everything required to switch over to the new Studs and freshen and rebuild your Rockers at the same time. The COMP Cams 1/2" Rocker Stud and Trunnion Retro-Fit Kit can also be used to retro-fit old Pro Magnumâ„¢ or old Hi-Tech Stainless Steel Rockersâ„¢Provides a stiffer valve train to achieve maximum valve motion in SBC or BBC engines featuring Ultra Pro Magnumâ„¢ or Ultra Pro Magnumâ„¢ XD RockersDesigned first for NHRA Stock Eliminator