Grinding Wheel Grit Chart: Grits, Grades and Bonds Explained

A grinding wheel grit chart ranks abrasive grain size from coarse to fine. Lower grit numbers mean larger grains, faster stock removal and a rougher finish. Higher numbers cut slower and leave a finer surface. A grade letter from A to Z shows how firmly the bond holds those grains. Whatever you pick, the wheel's marked maximum RPM must meet or beat your tool's speed.

Key Takeaways

• Lower grit is coarser and faster. Higher grit is finer and slower.
• Grade letters run from soft (A to H) to hard (Q to Z). They describe bond hold, not grain sharpness.
• Hard workpieces usually pair with softer grades, so dull grains release and fresh ones cut.
• Our grinding wheels are resin bonded, fiberglass reinforced T27 wheels for angle grinders. Their pages list max RPM, not grit or grade.
• Never run a wheel faster than its marked maximum RPM.

How do you read a grinding wheel grit chart?

Most wheel labels carry three codes: a grit number, a grade letter and a bond letter. The grit number is the abrasive particle size under the ANSI B74.12 sizing convention. The grade letter is the bond's hold on those particles. The bond letter names the material that binds them. The tables below take each code in turn.

A note on scope. These tables describe grinding wheels in general, including vitrified bench and surface wheels that we do not sell. Treat that material as reference. If you shop for a bench machine, our bench grinder reviews cover the tools.

What grit grinding wheel do you need?

Grit sets how fast a wheel removes metal and how smooth the surface looks afterward. Use these bands as a starting point, because pressure, wheel speed, dressing, contact area and the metal all change the result.

Grit for weld cleanup and shaping

Coarse and medium grits do the heavy work. On a bench wheel, 36 grit suits reshaping and 60 grit is a sound general choice. The trade is a rougher surface that you may need to clean up with a finer abrasive.

Grit for sharpening tools

Fine grits give control at an edge. A bench wheel in the 100 to 120 range is a common choice for sharpening, and 36 to 60 stays for reshaping a damaged edge. This is general reference guidance for bench wheels, not a Benchmark product recommendation.

Grit for blending and finishing

On an angle grinder, grit choice matters most for blending and finishing, where a flap disc usually serves better than a grinding wheel. Our flap disc grit guide walks through the sizes.

What does the grade letter on a grinding wheel mean?

Grade is bond strength, not grain sharpness. A soft grade lets dull grains break free so fresh ones take over, and a hard grade holds grains longer. The scale runs from A (softest) to Z (hardest). The grinding wheel specification sets where grade sits in the full marking.

Why hard steel often needs a soft grade

Grains dull as they cut. On hard steel, a soft grade sheds them, so the wheel keeps cutting instead of rubbing. A hard grade on the same job tends to glaze, run hot and discolor the work. Our guide to grinding wheel hardness covers the theory.

Softer workpieces flip the rule. They tolerate a harder grade, which keeps its shape longer, especially on a small contact patch.

Which bond type should you choose?

The bond is the last letter or letters in a wheel marking. It decides how rigid the wheel is, how it handles shock and which jobs it suits. Vitrified wheels are rigid and porous, which favors precise bench work. Resin bonds absorb shock, which suits the side loads of hand-held angle grinding.

Our grinding wheels use Bakelite resin and layers of fiberglass. They are reinforced resin wheels for angle grinders, not vitrified bench or surface wheels. To see that style in the catalog, browse our Type 27 wheels.

Which grain matches your metal?

Pick the metal first, then the grain. Grain letters in a marking include A for aluminum oxide, C for silicon carbide, Z for zirconia alumina and SG for ceramic.

Stainless steel and contamination

Iron particles left in a wheel can transfer to stainless and cause staining or corrosion later. Keep a wheel for stainless only, or choose one made for it. Our pipeline wheel pages say their highly refined ingredients will not contaminate stainless steel. For demanding production work, compare ceramic vs zirconia vs aluminum oxide.

Cast iron and silicon carbide

Silicon carbide cuts cast iron well because the grain is hard and sharp, and the metal is brittle. Use light, steady pressure and manage the dust. Our silicon carbide vs aluminum oxide comparison shows where each grain wins.

Aluminum and wheel loading

Aluminum is soft and ductile, so it smears into the wheel face instead of breaking into chips. The metal fills the gaps between grains, the wheel stops cutting and heat builds. A wheel made for aluminum resists this. Our T27 grinding wheel for aluminum blends aluminum oxide with silicon carbide for that job.

Why wheel color is not a spec

Wheel colors hint at grain types, but color is not a standard. Check the printed marking, the maker's data, the diameter, the arbor and the max RPM before you mount a wheel.

What is the max RPM for each grinding wheel size?

Max RPM falls as wheels get larger, which keeps rim speed in a safe range. This table lists the speed on each of our T27 pages, with surface speed in feet per minute (SFPM) worked out from it. It is also our grinding wheel size chart for angle grinder wheels.

SFPM = RPM x wheel diameter (in) x 3.1416 / 12. For the theory behind speed and pressure, read our RPM, grit and pressure guide.

The 4X ceramic row shows no figure because we are confirming its rating. Read the label on the wheel itself. Some of our wheels use a 5/8-11 threaded hub instead of a 7/8 inch arbor, so check your spindle thread before you buy.

Your grinder's no-load speed must stay at or below the wheel's number. OSHA states the same rule in 29 CFR 1910.215(d)(1): spindle speed must not exceed the maximum marked on the wheel.

What are the main grinding wheel types and shapes?

Shape decides which tool and guard a wheel fits. Grit, grade, bond and marked RPM then decide how it performs.

Grit and grade choices matter most on bench wheels for sharpening and shaping. On angle grinder wheels, metal and speed usually decide first. A straight wheel can look like a depressed center wheel, but they are not interchangeable.

How do you decode a full grinding wheel marking?

ANSI B74.13 sets the order of a marking: abrasive, grit, grade, structure, bond. Here is a sample, A 36 R 5 BF. It is a worked example, not one of our products.

• A: the abrasive, aluminum oxide.
• 36: the grit, a medium grain.
• R: the grade, in the hard range (Q to Z).
• 5: the structure, or grain spacing. Many labels leave it out.
• BF: the bond, a fiberglass reinforced resinoid.

Our T27 pages list grain, size and max RPM instead of a full marking. For every position in the code, read how to read a grinding wheel spec.

Which Benchmark Abrasives grinding wheels fit common jobs?

Our grinding wheels are resin bonded, fiberglass reinforced Type 27 wheels for angle grinders. Our product pages list size, grain and max RPM, not a grit number or grade letter, so choose by size, speed and metal.

4-1/2 inch aluminum oxide T27 for steel and stainless

The 4-1/2 x 1/4 x 7/8 inch aluminum oxide wheel suits general grinding of carbon steel, stainless and other ferrous metals at up to 13,500 RPM. It fits angle grinders from 4-1/2 to 5 inches.

6 and 7 inch T27 for heavier removal

The 6 inch wheel is marked 10,200 RPM and the 7 inch wheel 8,600 RPM. The 7 inch page lists it for aggressive stock removal on a large angle grinder.

4X ceramic T27 for demanding ferrous work

The 4X wheel adds ceramic grain for a cooler cut on ferrous metals, including stainless. Confirm its marked RPM before mounting.

1/8 inch pipeline wheels for notching and light grinding

These 1/8 inch T27 wheels cut, notch and lightly grind stainless, carbon steel and other ferrous metals.

Flap discs when grit is the real decision

If your job turns on choosing a grit for blending or finishing, start with a flap disc instead of a grinding wheel.

Browse Benchmark grinding wheels by size and speed.

What do people ask about grinding wheel grit and grade?

What grit grinding wheel is best for sharpening tools?

For most tool sharpening, a bench wheel in the 100 to 120 grit range gives good edge control. Use 36 to 60 grit when you need to reshape or repair a damaged edge. Match the wheel's diameter, arbor, type and RPM rating to your bench grinder.

What does the letter grade on a grinding wheel mean?

The grade letter shows how firmly the bond holds the abrasive grains. It does not describe the hardness or sharpness of the grain. Soft grades (A to H) release dull grains sooner, and hard grades (Q to Z) keep them longer.

Is a higher grit number coarser or finer?

A higher grit number is finer. A lower number is coarser. A 36 grit wheel removes material quickly for shaping, a 60 grit wheel suits general grinding, and 100 to 120 grit gives more control for sharpening. Pressure, dressing and the metal also change the finish.

Should I use a soft or hard grade wheel for hard steel?

Use a softer grade for hard steel in most cases. A soft bond releases dull grains, so fresh sharp grains keep cutting cooler and the wheel glazes less. Wheel speed, coolant and contact area still matter, so follow the maker's guidance.

What grinding wheel should I use on stainless steel?

Use a wheel made for stainless, and keep it for stainless only when contamination matters. Particles from a wheel that has ground carbon steel can transfer to stainless and lead to staining or corrosion. Confirm the wheel type, guard and RPM match your grinder.

Why does my grinding wheel load up on aluminum?

Aluminum is soft and ductile, so it smears and packs between the abrasive grains instead of breaking into small chips. That cuts the wheel's bite and builds heat. Use a wheel made for aluminum, such as our T27 grinding wheel for aluminum, rather than forcing a steel wheel to do the job.

How do I find the max RPM of a grinding wheel?

Read the marked maximum RPM on the wheel label or blotter, then compare it with the no-load RPM on your grinder's nameplate. The wheel's number must be equal to or higher than the tool's. For our wheels, the max RPM also appears on each product page.

Can I put a bench grinder wheel on an angle grinder?

No. A bench wheel is built for a different machine, guard, mounting method and speed, even when the arbor appears to fit. Discard any cracked or dropped wheel, and follow the tool and wheel instructions plus OSHA and ANSI requirements.

Match grit to the finish you need, grade to the metal and bond to the tool, then keep tool speed at or below the wheel's marked max. Use this grinding wheel grit chart as a starting point and let the label decide. Browse our grinding wheels to find your size.