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115mm vs 125mm grinding disc

Updated: 21 October 2026

You have two depressed-centre wheels on the bench, both with a 22.23 mm hole, and you are about to put the larger one on the smaller grinder because the nut fits. That is the wrong test. A 115mm vs 125mm grinding disc choice is about the guard and the rpm mark, not the bore. This page says which Merryland pack matches which machine, and what Hilka cannot tell you from the listing alone. The scores for all three stay on the [grinding discs comparison](/hub/sanders/grinding-discs). Peter F. did not measure a guard with calipers in a lab. Figures are from the amazon.co.uk listings on 19 October 2026. A qualifying purchase can earn a commission at no extra cost to you.

You have two depressed-centre wheels on the bench, both with a 22.23 mm hole, and you are about to put the larger one on the smaller grinder because the nut fits. That is the wrong test.

Our top picks

Merryland Merryland 125 mm grinding wheels (10)

Best overall

Merryland Merryland 125 mm grinding wheels (10)
4.5/10about £17.90
View offer
Merryland Merryland 115 mm grinding wheels (10)

Rank 2

Merryland Merryland 115 mm grinding wheels (10)
6.8/10about £15.90
View offer
Hilka Hilka Turbo Flex grinding discs (5)

Best value

Hilka Hilka Turbo Flex grinding discs (5)
5.5/10about £10.02
View offer
On this page
  1. 1.Same hole, different guard
  2. 2.The rpm mark drops as the disc gets larger
  3. 3.Which box to open for the grinder you have
  4. 4.When the disc is proud of the guard

Same hole, different guard

Hand-held angle-grinder discs in both sizes use a 22.23 mm bore, also sold as 7/8 inch. The hole is why the wheels feel interchangeable. The guard is why they are not. A 115 mm disc, often called 4.5 inch, belongs on a 115 mm grinder. A 125 mm disc, often called 5 inch, belongs on a 125 mm grinder. If the wheel stands proud of the guard, you do not remove the guard and you do not grind the disc down to sneak it inside. The Merryland 115 mm listing is ten discs at £15.90, printed as 115 x 6.0 x 22.23 mm. The 125 mm listing is ten discs at £17.90, printed as 125 x 6.0 x 22.23 mm. Hilka is 115 x 6 mm only, five discs at £10.02, and the listing does not print the bore. Assume nothing about that hole until you read the ring.

The rpm mark drops as the disc gets larger

A larger disc has a higher surface speed at the same spindle rpm, so the maximum printed on the wheel is usually lower. Merryland's 115 mm bullets say 13,300 rpm. The 125 mm bullets say 12,250 rpm. Both claim EN 12413. The disc's mark must be at least the rated speed of the grinder you are fitting. A 125 mm wheel marked 12,250 rpm does not become safe on a faster 115 mm grinder because the hole matches. Hilka prints EN 12413 and no rpm, so it is not the same speed as Merryland. If the ring is missing or slower than the grinder, it stays off. Do not copy a Klingspor catalogue figure onto a Merryland or Hilka label.
Merryland Merryland 125 mm grinding wheels (10)

Testsieger

Merryland Merryland 125 mm grinding wheels (10)
4.5/10about £17.90
View offer

Which box to open for the grinder you have

If the guard is 115 mm, the Merryland 115 mm ten-pack is the top pick in this set. The grit field says 46 while the material line says A30R-BF. That clash does not make the 125 mm pack a substitute. Hilka at £10.02 is the best value only as grit 180, a finer finish than weld dressing, and only after the ring confirms bore and speed. If the guard is 125 mm, open the Merryland 125 mm ten-pack at £17.90. It does not win an award, because the reviews describe cutting and one report disputes the guard fit. A larger 125 mm range sits on 125mm grinding discs. Thickness, grit and the date are on the grinding disc buying guide. Who should skip each pack is on best grinding discs.

When the disc is proud of the guard

Do not run an oversize wheel with the guard off, and do not trim the abrasive to force a fit. A published review of the 125 mm Merryland pack describes discs about 2 mm too big for a 125 mm guard. Reject that wheel, or return the pack, and fit a disc that sits inside the guard you already have. A 115 mm disc on a 125 mm grinder is still the wrong diameter, even when the nut fits.

Common questions

Can a 125 mm grinding disc go on a 115 mm grinder?
No. The 22.23 mm bore can match and the wheel will still stand outside a 115 mm guard. Do not remove the guard to gain the extra reach. Buy a 115 mm disc, such as the Merryland pack marked 115 x 6.0 x 22.23 mm and 13,300 rpm.
Can a 115 mm disc go on a 125 mm grinder?
It is still the wrong diameter for that guard, even if the nut fits. You lose the size the 125 mm guard was built around. Inside this comparison, use the 125 mm Merryland pack and check it sits inside the guard when it arrives.
Why is the 125 mm rpm lower?
Merryland prints 12,250 rpm on the 125 mm pack and 13,300 rpm on the 115 mm pack. A larger diameter runs faster at the rim for the same spindle speed, so the wheel's maximum is usually lower. The disc must still be rated at least as fast as your grinder. Hilka prints no rpm.
Do both sizes share the same bore?
Merryland prints 22.23 mm on both the 115 mm and the 125 mm pack. That shared hole is why people swap them. Hilka's 115 mm listing does not print a bore, so you cannot claim 22.23 mm for that five-pack from the page alone. Read the metal ring before you order a spare flange.
Is the 125 mm pack the better buy because it has more reviews?
It has 1,074 reviews at 4.6, against 1,006 on the 115 mm Merryland pack, also at 4.6. The extra reviews do not change the guard. Many of them describe cutting rather than a 6 mm face. Pay £17.90 for the 125 mm box only when the grinder is 125 mm, and measure the disc against the guard.
What if the disc is 2 mm too big for the guard?
Do not run it with the guard off, and do not trim the abrasive to force a fit. A published review of the 125 mm Merryland pack describes that oversize. Reject the wheel or return the pack, then fit a disc that sits inside the guard you already have.

Related pages

How to use a grinding disc

Grinding discs

Best grinding discs: Merryland top pick for 115 mm

Grinding disc buying guide: diameter, grit and rpm

Grinding disc versus cutting disc: face or thin edge

Sources

Sources taken from the research digest. Prices, stars and review counts are the stored amazon.co.uk listing figures.

  1. HSE HSG17 — safety in the use of abrasive wheels (retrieved 19.10.2026)
  2. HSE — PUWER overview (retrieved 19.10.2026)
  3. FEPA — safety leaflet, bonded abrasives (retrieved 19.10.2026)
  4. Cutwel — expert guide to grinding discs (retrieved 19.10.2026)
  5. Cutwel — Klingspor A 24 R grinding wheels (retrieved 19.10.2026)
  6. Abrasives Safety — reinforced bonded wheels (retrieved 19.10.2026)