3 in. Carbon Steel Knot Wire Cup Brush

This is an awesome attachment that packs a huge punch. It easily removes rust and paint and will go to work on the metal below if you let it, so do be careful with outside corners, very easy to round those over accidently. I’m attaching a picture of the back of the box that does a better job explaining the difference between versions of cup brushes

This review is for the Milwaukee 3-inch Brush Knot Cup, model 5040. I purchased the 3-inch brush to use on a Milwaukee angle grinder, model 6141-30. I should note that I’m not a metal worker (professional or otherwise); rather I’m a DIY home owner and my review is from that standpoint. YMMV. The grinder is rated for 12,000 RPM and the 3-inch brush is similarly rated. It is critical, when using an angle grinder, not to use attachments which are not rated at a high enough speed. At 12,000 RPM things tend to disintegrate quickly if not properly designed and manufactured. There is a safety notice on the brush packaging noting that proper protection must be worn, including a respirator under some conditions. I use safety glasses and a full-face shield as well as heavy leather gloves. Wires tend to come loose on wire wheels mounted on angle grinders and can go deeper than one might expect into one’s hands. Of course, the guard was in place on the angle grinder when using the cup brush. The 3-inch brush mounted easily on the 6141-30 grinder (see photos) and dismounted as easily. I tested the unit on a metal door that needs refinishing; I wasn’t grinding down the metal per se, but rather getting the old finish off. This 3-inch brush on an angle grinder beat my old wire brush setup on a ½” drill hands down. Of course, a flat wire wheel is also used for such work as well as sanding disks. The cup design gets into cracks and crevices that the other attachments don’t do as well on – but make certain that the work piece is secured! The cup can grab the work and send it flying off. I didn’t have to “lean into” the grinder to get the job done, but you must maintain a good grip on the grinder and enough pressure so that the brush doesn’t go skittering off the work. Milwaukee notes that the product “is meant for cleaning castings, structural steel, and sheet metal”. The doors I’m working aren’t sheet metal, of course, but the principle seems to be the same – at any rate the brush worked on my application. On wood doors, probably not so much – Milwaukee can’t (or won’t) guarantee this product for that application. I have two doors left to do (and probably won’t finish before winter sets in) but from the admittedly limited workout I’ve given the Milwaukee 3-inch cup brush I don’t think I’ll wear it out before the jobs are completed. Not a tool that, as a DIY, I will use every day but one that I’m glad to have in my kit. HTH Regards, Jim

This Brush Knot Cup held up well to my old, rusty railings at my mid century home in the Upper Midwest. Loose rust and paint was easily removed from over 15 linear feet of railing. I was able to reuse the product on an additional project I had not even planned on getting to due to its durability and effectiveness.

I use this product a lot with my angle grinder to get rid of rust on metal surfaces; it works like a champ! I have a small-size Makita grinder, and at first could not find the right size brush to fit the metric threads. The sales person was extremely helpful in helping me find an adapter; much thanks!

Needed to remove calcium build up on a swamp cooler grate , nothing else had worked . This worked

I’m barely going anywhere with my projects, but I couldn’t do it without Home Depot and throwing my rims away

Excellent quality! Product made in USA, shameful that we can’t enjoy this type of quality anymore, we just have to pay premium price for a chinese made product that most of the time won’t last.

Frayed right away, it worked about as good ad a harbor freight one. I bought a DeWalt one and it was way better.

I use it to take tar off of metal on mobile home roofs.