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T29 vs T27 flap disc

Updated: 21 October 2026

The two discs in your hand are both 125 mm, and one will skate across a weld while the other digs a hollow into a panel. T29 vs T27 flap disc is that shape difference. Type 29 is conical. Type 27 is flat. The angle you hold, and the job in the vice, decide which one earns its keep on a UK 125 mm grinder. This sits beside the [125 mm flap disc comparison](/hub/sanders/flap-discs-125), where six of the seven packs are Type 29 and one is Type 27. We did not run a lab comparison. If you buy through our links, a qualifying purchase can earn us a commission at no extra cost to you.

The two discs in your hand are both 125 mm, and one will skate across a weld while the other digs a hollow into a panel. T29 vs T27 flap disc is that shape difference. Type 29 is conical. Type 27 is flat.

Our top picks

Merryland Merryland 40 grit 10-pack

Best overall

Merryland Merryland 40 grit 10-pack
9.4/10about £12.90
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Merryland Merryland 40 grit 20-pack

Best value

Merryland Merryland 40 grit 20-pack
9.0/10about £21.90
View offer
Flintronic Flintronic 125 mm flap disc

Rank 3

Flintronic Flintronic 125 mm flap disc
7.4/10about £12.99
View offer
On this page
  1. 1.What the two profiles change on the steel
  2. 2.When Type 29 is the disc to mount
  3. 3.When Type 27 is the flatter choice
  4. 4.How to tell them apart in the listings

What the two profiles change on the steel

A Type 29 flap disc leans the flaps out. At about 15 to 25 degrees, the outer grit cuts a weld toe, a cut edge, or rust on a curve. Laid flat, those tips glaze. Empire Abrasives’ account is the short version: the conical face removes stock at an angle, and the flat face covers area. A Type 27 disc presents a flatter layer. More of the diameter can touch a panel you want blended rather than scooped. Used on its rim to chase a proud bead, it cuts slowly and the edge can groove. Bore, diameter and the rpm rule do not change with the profile. About 12,200 rpm at 80 m/s is still the figure. Profile is not a speed rating. Grit sits on top of shape. A Type 29 in 120 grit will not remove a weld the way 40 grit will. Shape picks the contact. Grit picks the depth. The 125mm flap disc buying guide keeps those as separate checks.

When Type 29 is the disc to mount

Mount Type 29 when the metal sticks up: weld beads, spatter you are allowed to remove, cut edges, and heavy scale. Hold a gap under the back of the disc so the outer flaps do the work, and move along the bead. Parked on one spot, the same disc dishes the panel. In this set the Type 29 packs are the three Merryland cartons, plus GZKTY, MIDO and Gmozkrn. Merryland’s 40 grit 10-pack at £12.90, 4.6 from 330 reviews, 12,250 rpm, is the one we would mount first on a weld, and it is the top pick on the best 125mm flap disc page. The 80 grit pack is the same conical idea once the bead is down. The 20-pack is the same profile if you grind welds all month. GZKTY and MIDO are Type 29 mixes, so the coarse discs are the weld discs and the 120 grit discs are the blend. Gmozkrn is Type 29 in aluminium oxide, without 40 grit, with no rpm in the extract and four reviews. Conical shape alone does not make that nine-pack the weld disc.
Merryland Merryland 40 grit 10-pack

Testsieger

Merryland Merryland 40 grit 10-pack
9.4/10about £12.90
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When Type 27 is the flatter choice

Mount Type 27 when the job is a face rather than an edge. Paint on a flat bracket, light rust on plate, a flange you need even: more flaps in contact, less risk of a groove from the rim. Flat does not mean you press until the motor note drops. Flintronic is the Type 27 pack here. It is £12.99, 4.3 from 43 reviews, aluminium oxide, listed at 13,300 rpm, with four discs at 40 grit and two each of 60, 80 and 120. A reviewer got old paint off and said they do not last long. The title prints Ø125 mm x 22 mm, so you confirm the hub on a 22.23 mm spindle. Your grinder’s plate still has to be at or under the disc. Choose Flintronic for flatter contact after you check bore and speed in the hand. Leave it on a weld bead. A Type 27 aluminium oxide disc knocks a bead down more slowly, and hotter, than a 40 grit zirconia Type 29. It is the only Type 27 in this seven.

How to tell them apart in the listings

Trust the title when the specification field is vague. Merryland’s 80 grit pack says T29 in the title and ANSI B7.1-2010 in the profile field. ANSI B7.1 is not a shape. The title is the shape. GZKTY’s profile line says zirconia corundum T29, which mixes grain and profile, and the shape is still Type 29. MIDO and Gmozkrn say Type 29. Flintronic says T27. If a listing says both, do not average them. Buy the profile the photograph and the title agree on, then confirm on the disc label. The way you hold the grinder changes with that label, which is the practical half of the how to use a flap disc page. A Type 29 that has already cut mild steel is still the wrong last disc on stainless, conical or not.

Common questions

What is the difference between a T29 and a T27 flap disc?
Type 29 is conical and cuts on the outer flaps at about 15 to 25 degrees. Type 27 is flatter and covers more of a broad surface. The profile does not change the speed rule.
Which should I buy for grinding welds?
Buy a Type 29 in 40 grit if the bead is still proud. In this set that is a Merryland zirconia T29 with 12,250 rpm on the listing. A Type 27 is the slow, hot way to take a bead down.
Is the Flintronic pack the only Type 27 here?
Yes, among the seven listings kept for this comparison. The Merryland packs, GZKTY, MIDO and Gmozkrn are Type 29. Flintronic is Type 27, aluminium oxide, at £12.99, with 13,300 rpm and a title that prints a 22 mm bore.
Can I use a Type 29 flat against the metal?
The outer flaps then take all the work, glaze, and people press harder. Hold the conical disc at roughly 15 to 25 degrees. If you need full-face contact, change to a Type 27.
Does Type 29 last longer than Type 27?
Life follows grain, pressure and grit more than the profile name. A Flintronic reviewer said the Type 27 discs do not last long on paint. A Merryland 80 grit reviewer thought the Type 29 wore slightly quicker. Neither line is a lab result.
Why does one Merryland field say ANSI instead of T29?
The 80 grit title says T29 and the profile field says ANSI B7.1-2010. Use the title for the shape. That American marking is not an EN 13743 claim and it does not tell you the working angle.

Related pages

Flap disc for stainless steel

Flap discs 125

Best 125mm flap disc: Merryland packs, from £12.90

125mm flap disc buying guide: bore, speed and grit

How to use a flap disc safely on a UK 125 mm grinder

Sources

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

  1. CCR Mag — abrasive wheel regulations (retrieved 21.10.2026)
  2. FEPA flap disc safety leaflet (retrieved 21.10.2026)
  3. oSa EN 13743 marking guide (retrieved 21.10.2026)
  4. Eisenblätter UK — flap disc speed table (retrieved 21.10.2026)
  5. Bosch Professional UK — 125 mm Type 29 flap disc (retrieved 21.10.2026)
  6. Empire Abrasives — T27 vs T29 (retrieved 21.10.2026)