What Size Grinding Discs Do You Need for Your Grinder?

Start with the label on your grinder

The fastest way to find your disc size is to read the nameplate on the grinder body or the first page of the manual. It lists the maximum disc diameter, often as inches or millimeters, along with the spindle thread and the no-load speed in RPM.

This applies to every brand, Milwaukee included. Milwaukee makes grinders in more than one size, so a model name alone is not enough. Check the printed disc size for your exact tool.

Three numbers matter: disc diameter, arbor (center hole) size and max speed. If a disc matches on all three, it is a correct fit.

Common grinding disc sizes

Angle grinders come in a handful of standard sizes. The metric and inch figures below are the common pairings, so you will see both on packaging.

The 4 1/2 inch size (115 mm) is the one most home and shop users own. The 5 inch size (125 mm) uses the same arbor in most cases, which is why some discs are sold for both.

Match the arbor hole, not just the diameter

The arbor is the center hole of the disc. In the flap disc data we compare, most discs use a 7/8 inch arbor, which is the common size for grinders with a flange and locking nut. The Panlen listing gives the same size as 22.2 mm, so you may see either unit.

The exception in our data is the PFERD POLIFAN CURVE, which uses a 5/8-11 thread. That type threads directly onto the spindle instead of sitting on a flange, so it only suits a grinder with a matching 5/8-11 spindle.

If your grinder has a 5/8-11 spindle, a 7/8 inch disc will not mount correctly. If it uses a flange and nut, a threaded disc will not fit. Read the listing before you order.

Check the max speed rating

Every disc has a maximum safe speed printed on it. Among the discs on our best flap discs page, most are rated for 13300 RPM, and the range runs from 13000 to 15000 RPM.

Your grinder's no-load RPM must not exceed the disc's rating. If the grinder spins faster than the disc allows, the disc can break apart while it spins.

If a disc lists a speed in meters per second, the 80 m/s figure on some listings pairs with the 13,300 RPM rating on a 4 1/2 inch disc.

Which size should you choose if you can fit more than one?

Many grinders accept a smaller disc than their maximum, but you should stay within the guard's rated size. Never put a larger disc on a grinder than the guard and nameplate allow.

Some discs are made to fit two grinder sizes. The Benchmark Abrasives 40 grit T29 disc, for example, lists compatibility with 4 1/2 inch and 5 inch grinders and any 7/8 inch arbor grinder, and it names Milwaukee among the brands. That is helpful if you own one of each size, but still confirm your own model's disc size first.

Here is a quick way to choose:

Use these steps in order:

• Read your grinder's nameplate for max disc diameter.
• Confirm the arbor: 7/8 inch for most, 5/8-11 for threaded spindles.
• Compare the disc's max RPM with your grinder's no-load RPM.
• Pick the disc shape and grit for the job.
• Check the guard is the right size and fitted before you start.

Pick grit and shape after the size is settled

Once the size fits, choose the grit. Per our buying guide, 40 grit cuts fast and leaves a rough surface, 60 grit balances removal and finish, and 80 and 120 grit blend and finish. Mixed packs of 40, 60, 80 and 120 grit, such as the 24-disc Pukamam set, help when a job needs several steps.

Shape matters too. A convex T29 disc is angled so the flaps meet the work at a working angle, such as 15 to 20 degrees in the EZARC listing, which helps on edges and weld seams. A flat disc suits flat surfaces.

For how many discs to buy, think in steps. A coarse pass, a middle pass and a finishing pass each use a different grit. The packs we list range from a single disc up to 60, so a one-job repair needs far fewer than a shop that grinds every day. Our flap disc comparison shows pack counts side by side.

Safety before you mount a disc

Unplug a corded grinder or remove the battery before changing a disc. Keep the guard on, and use the side handle.

Wear safety glasses or a face shield, hearing protection, gloves and a dust mask suited to the material. Grinding throws sparks and hot debris, so clear flammable items from the area.

After mounting, hold the grinder away from your body and let it run up to full speed for a short time before touching the work. Stop and replace any disc that is cracked, chipped or wobbles.

Frequently asked questions

Can I use a 5 inch disc on a 4 1/2 inch grinder?

Not unless the grinder and its guard are rated for it. The guard is sized for a specific disc diameter, and a larger disc can stick out past it.

Do all Milwaukee grinders take the same disc?

No. Milwaukee sells grinders in several sizes, so check the disc size printed on your specific tool. Many take a disc with a 7/8 inch arbor, but confirm it for your model.

Is a flap disc the same as a grinding disc?

Not exactly. A flap disc has overlapping abrasive flaps and blends as it grinds, while a traditional grinding wheel is a solid, rigid disc built for heavy removal. Both mount on an angle grinder and both need the right size and speed rating.

What does Type 29 mean?

Type 29 is a conical, angled disc shape. It lets the flaps meet the surface at an angle, which suits edges and welds.

Can I use a disc rated below my grinder's speed?

No. The disc's max RPM must be equal to or higher than your grinder's no-load speed, or the disc may fail in use.