Knotted vs Crimped Wire Cup Brushes for Angle Grinders

Which wire cup brush do I need? Start here

Pick a wire cup brush in three steps: the size your grinder can spin, the wire that matches your metal, then knotted or crimped for the job.

1. Check the speed. On a 4-1/2 in. angle grinder with a 5/8"-11 spindle, use a 3 in. cup. Every 3 in. cup we sell is rated 12,000 RPM.

2. Match the wire to the metal. Carbon steel wire for carbon steel. Stainless wire for stainless steel and aluminum.

3. Heavy or light?

   • Carbon steel, heavy (mill scale, slag, mortar): knotted 13F354, $23.52 each, min 2.

   • Carbon steel, light (paint, light rust, sheet metal): crimped 13D304, $20.40 each, min 2.

   • Stainless, heavy (heat tint, scale): knotted 13F314, $46.20 each.

   • Stainless or aluminum, light: crimped 13D314, $30.60 each.

   • Weld bead or tight corner: 13C130 knot wheel in a die grinder, $19.80 each, min 2.

Should I use a knotted or crimped wire cup brush?

Use a knotted wire cup brush when the dirt is hard and the metal is thick, and a crimped one when the surface is thin or the job is light. A knot-twisted brush bundles its wires into stiff strands that strike like small hammers, so it breaks up mill scale, slag and flaking rust. A crimped brush has single wavy wires that flex, so it follows the surface and leaves a finer, more even scratch.

If a crimped brush isn't cutting, don't lean on it. Pressing harder bends the wires sideways, and that is what snaps them. Switch to a knotted cup instead.

Wire wheel or cup brush: which goes on my angle grinder?

A cup brush is for flat or broad surfaces, and a wire wheel is for edges, corners and the weld bead itself. The cup's face covers a wide strip fast, which is why it's the pre-weld prep tool for plate and pipe. A knot wheel (or a narrow stringer-bead wheel) runs on its edge and gets into fillets and between weld passes.

We stock cup brushes for angle grinders, not threaded wheels. For bead and corner work, a 2-3/4 in. knot-twisted mounted wheel (13C130) in a die grinder reaches the same spots.

Which wire cup brush sizes are safe on a 4-1/2" angle grinder?

A wire cup brush is safe on your grinder only if its maximum RPM is at or above the speed on your grinder's nameplate. Most 4-1/2 in. grinders run 10,000 to 11,000 RPM with no load. Every 3 in. cup we sell is rated 12,000 RPM, so it fits. Most of our 4 in. and 5 in. cups are rated 8,600 RPM, which is for 7 in. grinders or variable-speed grinders turned down.

Ratings from Walter's spec sheet for each SKU, checked Oct 22, 2026. Always read the speed stamped on the brush and on your grinder.

Two more fit checks: the thread and the guard. US grinders use a 5/8"-11 spindle; European and many imported grinders use M14. A cup brush threads straight onto the spindle with no flange or nut. Keep the guard on, and make sure the cup spins without touching it.

Carbon steel or stainless wire: does it matter?

Yes. Use carbon steel wire on carbon steel only, and stainless wire on stainless, aluminum and other non-ferrous metals. Carbon wire leaves iron particles in stainless that rust within days and can fail a weld inspection. Keep stainless brushes for stainless work only. Walter makes it easy: orange hubs are carbon, blue hubs are stainless (on the ALLSTEEL line, dark grey and white).

Which wire thickness and trim length do I need?

Thicker wire and shorter trim make a stiffer, more aggressive brush. Our cups run from .0118 in. (fine crimp) through .015 and .020 in. (most knots) to .035 in. (13G554, the coarsest). A ring around the knots, as on 13G304, holds the wires tight so the brush stays stiff and sheds less. For mortar on rebar, pick .020 in. knot wire.

Which wire brush for a drill or die grinder?

For a drill or die grinder, use a mounted brush with a 1/4 in. shank, not a threaded cup. Our mounted wheels are rated 25,000 RPM. Use the 2 in. crimped wheel (13C120) for light cleaning and the 2-3/4 in. knot wheel (13C130) for welds and corners.

Which wire cup brush should I buy?

Buy the wire cup brush that matches your grinder, your metal and your job; these twelve cover every case above.

Prices from our catalog, Oct 22, 2026.

From the shop floor

“When we’re prepping plate or pipe, the cup brush does the heavy lifting. That wide face clears a strip of mill scale in one pass. But a cup won’t get down into a fillet. For that, and for cleaning between passes, you want a knot wheel or a narrow stringer-bead wheel running on its edge."

David Castro, President, Eldorado Tools

Related guides: Which Grinding Wheel for Angle Grinder Work, Flap Disc vs Grinding Wheel on a Weld and Cut Off Wheels: .045 vs 1/16 vs 1/8. Shop all wire brushes.

Not sure which brush fits your grinder? Send us the grinder's model number and we'll match it.

Sources: Walter product spec sheets for each SKU listed (max and recommended speed, trim, wire size); Eldorado Tools catalog prices, Oct 22, 2026.

Change log: Oct 22, 2026, first draft.