The T-3 Series Roller J-Hooks makes aligning the barbell much easier. When racking the bar onto the roller, the roller slides the bar into the perfect position, and then the lifter can easily position the bar from side to side to center the bar in the T-3 Series Power Rack. Each J-Hook fits securely in place so you can focus on your workout without having to worry about the possibility of hook slippage or movement. Featuring heavy-duty nylon rollers and UHMW plastic on the backplate, lip, and frame, helping preserve your bars knurling and rack from being damaged. Additionally, the T-3 Series Roller accepts all bar sizes from standard to large squat bars.UPDATED VERSION: Featuring UHMW plastic on the implement's frame to prevent the rack from being damaged. Additionally, we have replaced the M12 front nut with a flush fastener to prevent your bar from being damaged.