125mm flap disc buying guide
Updated: 21 October 2026
You have a 125 mm angle grinder and a weld, a rust patch, or a painted bracket that a rigid grinding disc would dig into. A 125mm flap disc blends while it cuts, and the disc that fits is settled by bore, speed and grit before any star rating. This checklist covers the seven amazon.co.uk packs in our [125 mm flap disc comparison](/hub/sanders/flap-discs-125). It was updated on 19 October 2026 from those listings and from public UK guidance. We did not run a lab test. If you buy through our links, a qualifying purchase can earn us a commission at no extra cost to you.
You have a 125 mm angle grinder and a weld, a rust patch, or a painted bracket that a rigid grinding disc would dig into.
You have a 125 mm angle grinder and a weld, a rust patch, or a painted bracket that a rigid grinding disc would dig into. A 125mm flap disc blends while it cuts, and the disc that fits is settled by bore, speed and grit before any star rating. This checklist covers the seven amazon.co.uk packs in our 125 mm flap disc comparison. It was updated on 19 October 2026 from those listings and from public UK guidance. We did not run a lab test. If you buy through our links, a qualifying purchase can earn us a commission at no extra cost to you.
Our top picks
| Badge | Product | Max speed | Profile | Grit | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Merryland Merryland 40 grit 10-pack | 12,250 rpm | Type 29 | 40, single grit | 9.4 | about £12.90 | View offer |
| Best value |  Merryland Merryland 40 grit 20-pack | 12,250 rpm | Type 29 | 40, 20 discs | 9.0 | about £21.90 | View offer |
 Flintronic Flintronic 125 mm flap disc | 13,300 rpm | Type 27 | 40/60/80/120 | 7.4 | about £12.99 | View offer |
On this page
What a 125 mm flap disc is doing
A flap disc is coated abrasive flaps on a fibreglass or plastic hub, for an angle grinder rather than a random-orbit sander. On mild steel it knocks a weld bead down and takes rust back, where a grinding disc would leave a flat scar. The diameter has to be 125 mm. A 115 mm disc sits inside a 125 mm guard, and a 50 mm die-grinder wheel will not mount on this spindle.
The usual bore is 22.23 mm. Treat a title that prints 22 mm as a question. The Flintronic title writes Ø125 mm x 22 mm, so you look at the hub before you tighten the nut. Zirconia, also sold as zirconium or zirconium corundum, is the metal grain on the Merryland, GZKTY and MIDO packs. Aluminium oxide is what Gmozkrn and Flintronic list, and it is the softer choice for wood, paint and light metal. That split is how these grains are sold, not a timed test of these seven cartons.
Bore, speed and the mark on the disc
The grinder’s no-load speed must not exceed the maximum printed on the disc. For a 125 mm flap disc, the figure often quoted at 80 m/s is about 12,200 rpm, which is Eisenblätter’s UK table, and a Bosch Professional Type 29 example is marked 12,250 rpm. Merryland prints 12,250 rpm. MIDO prints 12,200 rpm. GZKTY and Gmozkrn do not show a maximum rpm in the extracted fields, so the label in the packet is the speed you can trust. Flintronic lists 13,300 rpm, above that 12,200 rpm table. A higher mark is not a reason to run the grinder faster. Stay at or under the lower of the two numbers.
EN 13743 is the marking FEPA expects: size, maximum speed, and the standard name. Do not assume a budget pack prints it. None of these seven was scored as if the mark were present. If you employ people to use abrasive wheels, PUWER 1998 requires training and a risk assessment. A home garage is not that employment case. Keep the guard on, and do not swap a flap disc into a cutting-off job. Type 29 is conical and Type 27 is flatter, including the 15–25° contact on a Type 29 face, on the T29 vs T27 flap disc page.
Grit, grain and the single number Amazon shows
Forty grit is the coarse cut for a weld bead or heavy rust. Sixty to 80 grit is the blend once the high metal has gone. One hundred and twenty grit is a finish before paint, and it is slow on a bead. A mixed carton looks convenient until the Amazon grit field stores only one of the grits. GZKTY’s field shows 40 while the title is 40/60/80/120. MIDO’s field shows 120 for the same kind of mix. Gmozkrn’s field shows 120 on a 60/80/120 nine-pack. Flintronic is the exception: four discs at 40 grit and two each of 60, 80 and 120.
Merryland sells 40 grit and 80 grit as separate 10-packs at £12.90, and a 20-pack of 40 grit at £21.90, so you know which sleeve you are opening. Zirconia on those discs is the grain we would rather see on steel than the aluminium oxide on the two cheaper mixed packs. Several titles name stainless steel, and none of the extracted fields say the grain is iron-free. That limit is the flap disc for stainless steel page.
How the seven packs split on those checks
Shelf prices in the October 2026 scrape run from £12.90 to £24.99. The Merryland 10-packs put 12,250 rpm on the listing. The 20-pack of 40 grit is about £1.10 a disc if you will use them. GZKTY at £18.99 has no rpm in the extract. MIDO at £24.99 prints 12,200 rpm on 16 reviews. Flintronic is the Type 27 mix. Gmozkrn has four reviews and a review title about unmarked grits.
A first pack for welds is the single 40 grit Merryland. Mounting sits on the how to use a flap disc page.
Common questions
Will this disc fit my 125 mm grinder?
Yes, if it is sold as 125 mm for a 125 mm grinder and the bore is 22.23 mm. A title that prints 22 mm, as Flintronic does, still needs a check on the spindle.
What grit should I buy first?
Start at 40 grit when the weld or rust is still proud, then 60 or 80 to blend, and 120 before paint. On GZKTY, MIDO and Gmozkrn the grit field stores only one of those numbers.
What rpm should be printed on the disc?
About 12,200 rpm is the figure often given for 125 mm at 80 m/s. If the listing is blank, as with GZKTY and Gmozkrn, use the mark on the disc. Stars do not tell you the speed.
Is Type 29 the right shape for welds?
Type 29 is the conical face people use on weld beads at roughly 15 to 25 degrees. Type 27 is flatter. Flintronic is the only Type 27 pack in this set.
Can I use these on stainless steel?
Some listings name stainless steel. None of the extracted fields say the abrasive is iron-free. If a later rust spot would matter, the word in the title is not enough.
Why does Amazon show one grit for a mixed pack?
The grit field stores one number, often 40 or 120, even when the title lists several. The pack contents are in the title. Only Flintronic states how many discs of each grit are in the ten.
When should I throw a disc away?
Stop when the flaps are torn, glazed, or worn down to the backing, or if the disc was dropped or cracked. A worn 40 grit disc does not turn into an 80 grit disc. Fit a fresh one of the grit you still need.
Related pages
Sources
Sources taken from the research digest. Prices, stars and review counts are the stored amazon.co.uk listing figures.
- CCR Mag — abrasive wheel regulations (retrieved 21.10.2026)
- FEPA flap disc safety leaflet (retrieved 21.10.2026)
- oSa EN 13743 marking guide (retrieved 21.10.2026)
- Eisenblätter UK — flap disc speed table (retrieved 21.10.2026)
- Bosch Professional UK — 125 mm Type 29 flap disc (retrieved 21.10.2026)
- Empire Abrasives — T27 vs T29 (retrieved 21.10.2026)