My wire wheel preference for the 4-1/2" grinder is about a 2-5/8" Twist Knot Cup Brush in either .35mm or .50 mm wire. The .35 gives a slightly softer finish. Both of these give good scale removal and finish. Anything much larger causes too much wobble and danger on a 4-1/2" grinder. I generally get the Hawk brand from MSCDirect.com.