Knurling is used to enable unrestricted pivoting of the polyurethane bush around the anti-roll bar. The knurling has two inherent design advantages. The knurling reduces the surface area of polyurethane in contact with the crush tube. This reduction in surface area results in less frictional forces being developed. The SuperPro knurl bore keeps the lubricating grease intact for the life of the bushing, and eliminates the necessity for periodic re-greasing. All SuperPro anti-roll bars come with SuperPro's anti-roll bar bushes (where needed) but they are also available to purchase separately for your standard or aftermarket roll bars.