Short answer: Two numbers decide it. The outer diameter must suit your grinder's guard, and the arbor hole in the middle must sit on your spindle. Our discs are 4 inch outer diameter with a 5/8 inch arbor, which is the standard combination for common angle grinders.
What is an arbor, in plain terms?
The arbor is the hole in the middle of the disc. It slides over the threaded spindle of your grinder, and a flange and nut clamp it in place.
Get it wrong in one direction and the disc will not go on. Get it wrong in the other and it rattles off-centre, which vibrates, cuts badly and stresses the disc.
There are only two measurements that matter, and both are printed on the disc.
The two numbers you need
Outer diameter. How big the disc is across. Common sizes are 4, 4.5, 5 and 7 inch. This has to match what your guard and tool were designed for. A disc that is too large will not fit under the guard, and a smaller one loses reach and depth.
Arbor hole. The hole in the centre. On small grinders the usual sizes are 5/8 inch and 7/8 inch.
Our discs are 4 inch outer diameter, 5/8 inch arbor hole, 0.04 inch thick, rated to 12,225 RPM. That is the standard fit for common angle grinders and works across DeWalt, Milwaukee, Makita, Bosch and more than 35 other brands.
How do I check what my grinder takes?
Three places to look, in order of speed:
- The disc that is on it now. The size is printed on the label of almost every disc, usually as something like "4 x .040 x 5/8". First number is diameter, last is arbor.
- The guard. Most guards carry a stamped maximum disc size.
- The manual, or the plate on the tool body. This also gives you the maximum RPM, which matters just as much.
If the tool is secondhand and unlabelled, measure the spindle and the guard opening.
Why does maximum RPM matter?
Because it is a safety limit, not a suggestion.
Every disc is rated for a maximum speed. If your grinder spins faster than the disc is rated for, the disc is being pushed past what it was tested to survive. Our discs are rated to 12,225 RPM. Most 4 and 4.5 inch grinders run around 10,000 to 11,000 RPM, so they are comfortably inside that.
The rule is simple: the tool's speed must not exceed the disc's rating. Never the other way around.
What if my thread does not match?
Diameter and arbor cover the disc itself. The spindle thread is separate, and it is where accessories sometimes disagree with the tool. M14 is common, M10 turns up on some tools and attachments.
If you have a disc or accessory built for the other thread, an M14 to M10 adapter bridges it. It is machined from hardened steel so it stays true at speed, and it ships with the wrench and flanges.
Do I have to keep hunting for the spanner?
No. A quick-lock nut replaces the standard flange nut and tightens by hand, so a disc change takes seconds. The knurled edge grips with gloves on, and it holds the disc flat so nothing wobbles at speed.
If you have ever abandoned a job because the pin spanner vanished, this is the fix.
A quick checklist before you fit a disc
- Outer diameter suits the guard
- Arbor hole matches the spindle
- Grinder's RPM does not exceed the disc's rating
- Disc is undamaged, with no cracks or chips
- Flange and nut are seated flat and tight
- Guard is on
The short version
Check two numbers, diameter and arbor, then check the speed rating. Our discs are 4 inch with a 5/8 inch arbor at 12,225 RPM, which covers common angle grinders across all the major brands.
See the discs: Cutting Discs for Angle Grinders
