115mm or 125mm angle grinder disc: how to tell which fits

You have a small angle grinder in the shed and an amazon.co.uk listing that offers a disc for 115–125 mm grinders. The question is whether your tool is a 115 mm or 125 mm angle grinder, and whether that disc matches it. Both sizes share the same bore, which is why the mismatch is easy to miss.

In short

A 115 mm disc belongs on a 115 mm (4.5 inch) grinder and a 125 mm disc belongs on a 125 mm (5 inch) grinder, even though both usually have a 22.23 mm bore. The guard is sized for one diameter. A title that says 115–125 mm is not proof that one disc suits both, so read the diameter cell before you buy.

Same bore, different disc

Small angle grinder discs in the UK almost always have a 22.23 mm bore, whether they are 115 mm or 125 mm across. Compel's UK size chart lists 22.23 mm for both, and Bosch Professional's UK range sells its Expert multi-material carbide disc in 115 mm and 125 mm as two separate part numbers with the same bore. A 125 mm disc will slide onto the spindle of a 115 mm grinder, and a 115 mm disc will slide onto a 125 mm one.

That shared bore does not make the sizes interchangeable. The guard, the motor speed and the flange are chosen for one disc size. How to match saw blade bore and diameter covers 22.23 mm, 20 mm, 16 mm and 30 mm.

A 4.5 inch grinder is the 115 mm class, because 4.5 inches is about 114 mm. A 5 inch grinder is the 125 mm class, because 5 inches is about 127 mm. Translate the inch size, then shop by 115 or 125. The bore only says a disc can be mounted.

The guard is the test

The guard decides the diameter. A 115 mm grinder is supplied with a guard for a 115 mm disc. A 125 mm disc either will not let that guard close, or leaves the rim outside the cover. Manuals tell you to use only the diameter the tool and its guard are designed for, and to keep the guard fitted. If the guard will not quite close, the disc is wrong.

Hold the disc against the outside of the guard, centre to centre, before you mount anything. If the edge reaches beyond the guard's rim, it is the wrong diameter. A 115 mm disc on a 125 mm grinder will sit inside the guard, but you lose cutting depth and the rim runs slower than the tool was designed for. Some makers allow that and some do not, so check the manual. Never fit a disc larger than the guard was built for.

Titles that span both sizes

Listings often put both sizes in the title: 115–125 mm, for 115/125 mm angle grinders, or 4.5 / 5 inch. A title is written to be found, not to be the specification. On amazon.co.uk, open the diameter cell and the variant selector above the price. Variant pages can share one title.

In our 125 mm wood cutting disc comparison, an Oiieco listing's title said 115–125 mm, but the diameter cell said 125 mm. A separate 115 mm variant existed under its own ASIN and has since been removed, so the page you land on today is the 125 mm disc. Trust the title on a 4.5 inch grinder and you receive a disc the guard was not built for.

On one VBVOO listing in the same set, the compatible-devices line names a 4.5 inch grinder and a 125 mm disc together. Those two facts contradict each other, because a 4.5 inch grinder is a 115 mm tool. Believe the diameter figure and treat the compatibility line as marketing copy. If the diameter cell is missing or disagrees with the images, ask the seller or pick a listing that states it plainly.

Speed marks are not identical

A bigger disc travels faster at the rim for the same rpm, so makers rate larger discs for a lower maximum speed. Compel's UK chart lists about 13,300 rpm for 115 mm and about 12,200 rpm for 125 mm. Treat those as typical chart figures. The rating on the disc must be at least the no-load speed on your grinder's plate. A 115 mm grinder often runs faster than a 125 mm one, so a larger disc on a smaller tool can be over-speed.

Not every amazon.co.uk listing states a maximum rpm. The Bosch Expert Carbide Multi Wheel 125 mm gives the diameter, the 22.23 mm bore and a 1 mm thickness, but no rpm figure. Check the disc when it arrives. If it has no speed mark, do not use it.

What not to copy from a review

Reviews help with how long a disc lasted and whether it wobbled. They are not a guide to modifying the grinder. One UK review of a Chersun disc describes fitting a 125 mm disc to a 115 mm Einhell by changing the guard, with a reported depth of roughly 20 to 30 mm. That is not a method. The guard is a safety part chosen for that tool's speed and size.

The extra depth is about 5 mm in theory, because the radius grows by 5 mm. The guard and the housing take some of that back. It is a reason to buy a 125 mm grinder, not to adapt a 115 mm one. Some listings sell a toothed 125 mm disc as a wood blade for an angle grinder. The Office for Product Safety and Standards warns in PSA5 that toothed attachments can kick back. Toothed blades on an angle grinder sets out what that means. Skip any tip that means removing, bending or swapping a guard.

A five-minute check before you order

You can settle the 115 or 125 question in about five minutes with the grinder in front of you.

1. Read the plate for diameter and no-load speed. 115 mm or 4.5 inch means 115 mm discs. 125 mm or 5 inch means 125 mm discs.
2. Confirm the supplied guard is fitted, and hold a disc you own against it.
3. On amazon.co.uk, read the diameter cell and the bore. You want your diameter and 22.23 mm, unless the manual says otherwise.
4. Check the size selector above the price. One title can cover several variants.
5. If the listing states a maximum rpm, compare it with the plate. If it does not, read the disc before first use.
6. Use a disc type the maker allows, and avoid toothed saw blades on an angle grinder.

For timber on a 5 inch grinder, our 125 mm wood cutting disc comparison ranks the amazon.co.uk options. The top pick is the Bosch Expert Carbide Multi Wheel 125 mm, one toothless carbide disc with a 22.23 mm bore, at about £15.96, rated 4.7 from 1,407 reviews. It suits a 125 mm grinder where the maker allows a carbide multi-wheel and the guard fits. It does not suit a 115 mm grinder. Per-disc maths for this single disc are in what a 125 mm wood cutting disc costs.

If the cut needs to be long and straight, a grinder of either size may be the wrong tool. The saw accessories hub covers circular saw blades and guide rails for that work.

How we checked

Peter F. is the editor for DIY and tools at productscompared.co.uk. We compared amazon.co.uk listings in the 125 mm wood cutting disc set against Compel's size and speed chart, Bosch Professional's UK range page and the OPSS PSA5 notice. We did not lab-test any disc or grinder. Prices and ratings are the October 2026 amazon.co.uk figures and can change. A qualifying purchase through our links can earn us a commission at no extra cost to you.