4.5” x 4” x 3/4” quad key shaft Nylon Wire Brush Drums by Black Hawk Abrasives are designed for removing scale and rust on uneven surfaces, including surfaces with nuts, bolts, brackets or rivets, without catching edges. Each 4-1/2 inch diameter scale wire drum is manufactured with abrasive-impregnated gray nylon bristles and sufficient void area (areas without bristles). The bristles are coarse, yet flexible allowing for them flex around imperfections, nuts and bolts without getting caught and damaging the grinder, drum or work piece. In addition to providing flexibility, the void space promotes airflow which prolongs the useful life of the wheel and reduces heat buildup that may damage a work piece. Additionally, BHA's nylon drums can operate bi-directionally so if the bristles become too lopsided, simply flip the drum over for a fresh, coarse Nygrind. With it's open brush design and flexible nylon bristles, the 4.5 inch black hawk abrasives nylon wire abrasive drum is perfect for the following applications: Removing rust, scale or other imperfections around nuts and bolts that would destroy other abrasive drums or discs. Specifically, cleaning rust off of frames and prepping the surface for a rust inhibitor. This drum is affixed with a hub that fits 3/4 inch keyed shaft and is made to be used on surface finishing machines and linear grinding machines (A.K.A. Burnishers, burnishing machines, contouring grinders, etc.)