Grit guide
Flap disc grit guide: choosing between 40, 60, 80 and 120
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Grit decides how fast a flap disc removes material and how fine the surface ends up. Too fine wastes time; too coarse leaves deep scratches and extra passes.
Based on Tyrolit documentation, this guide covers grits, grain types, the 27A and 28A shapes and the right coarse-to-fine sequence.
Key takeaways
- Tyrolit recommends grits 40/60 for high stock removal and 80/120 for fine grinding.
- Zirconia (ZA) is the grain for stainless steel and cast materials; aluminium oxide (A) for steel and non-ferrous metals.
- Shape 27A works at 15–20°, straight 28A/28N at 0–15°; never grind with the periphery of the disc.
- Move from coarse to fine step by step and remove the previous scratch pattern completely.
What the grit number means
The grit number indicates the size of the abrasive grains: the lower the number, the larger the grains, the more aggressive the removal and the deeper the scratches.
Coated abrasive grits are often written with a P prefix (P40, P80), after the FEPA scale. Tyrolit catalogues print the grit without a prefix, straight after the grain type (for example ZA 40): 40, 60, 80 and 120 for metal flap discs. Letters after the number are not the grit, and in Tyrolit codes such as ZA-P43N the letter P denotes the PREMIUM line.
Grit chart: which grit for which job
On almost every flap disc page of the Tyrolit 2026 catalogue the rule is the same: 40/60 for high stock removal, 80/120 for fine grinding.
| Grit | Tyrolit classification | Typical jobs | Next step |
|---|---|---|---|
| 40 | Pre-grinding, high stock removal | Heavy weld seams, thick rust and mill scale, rough bevels | 60 or 80 |
| 60 | Semi-finish grinding, high stock removal | Levelling welds, removing rust and paint, breaking edges | 80 |
| 80 | Semi-finish grinding, fine grinding | Smoothing ground areas, removing 40/60 scratches, preparing for paint | 120 |
| 120 | Finish grinding | Even surface on steel and stainless, last step before painting | Finer abrasives, only if the surface requires it |
Not sure where to start?
Grit 60 is a balanced starting point for many metal jobs: it removes material reasonably fast and leaves a surface that is easy to finish with 80 or 120.
Grain type: A, ZA, CA or ZACA
Grit is the size of the grains; grain type is what they are made of and which material they suit.
On stainless steel, disc purity matters as much as grit: Tyrolit states that chemical purity prevents corrosion, rust spots and reduced fatigue strength. A disc without an identifiable manufacturer gives you no such statement.
- A, aluminium oxide: for steel, cast steel and non-ferrous metals.
- ZA, zirconia: for stainless steel and cast materials. On stainless, choose flap discs for stainless steel or 2in1 discs; for the PREMIUM 2in1 disc, Tyrolit states the chemical purity described above.
- CA, ceramic: maximum stock removal and self-sharpening grain, for demanding work on stainless steel and non-ferrous metals.
- ZACA, zirconia plus ceramic (TWINFLAP): a grain combination for the highest aggressiveness, according to Tyrolit.
- C, silicon carbide: for stone and glass; here 60/80 are used for removal and 120–400 for finishing.
See also: Abrasives for stainless steel
Shape 27A or 28A: working angle and backing
Tyrolit names its flap disc shapes in its own system: 27A is the angled, depressed-centre profile with the working angle built in, and 28 is the straight profile; the letter usually indicates the backing (A fibreglass, N plastic, NF natural fibre), while 28S is the flexible SOFTJOB version. When comparing catalogues, check the profile and the specified angle, not just the number.
A fibreglass backing wears down with the flaps and does not scratch the workpiece; a plastic or natural-fibre one can be trimmed so the flaps are fully used.
- 28NF: straight profile with a natural-fibre backing that makes reducing the diameter as easy as possible.
- 28S SOFTJOB: a different flap arrangement for much greater flexibility; suited to contours, profiled surfaces, railings, rust and paint residue.
| Shape | Profile and backing | Working angle | Best for |
|---|---|---|---|
| 27A | Depressed centre, fibreglass backing | 15–20°, set by the disc shape | Surface grinding, levelling welds |
| 28A | Straight profile, fibreglass backing | 0–15° | Edge and surface grinding, bevelling |
| 28N | Straight profile, plastic backing that can be trimmed | 0–15° | Using the abrasive flaps completely |
See also: Cutting vs grinding vs flap disc
Coarse to fine: sequence and technique
Good results come from a logical sequence of discs. Start with the grit that removes the defect in reasonable time, then move to finer grits step by step.
- Step 1, removal: 40 for heavy welds, thick rust or mill scale; 60 for moderate defects.
- Step 2, smoothing: 80 removes the deep scratches left by 40 or 60.
- Step 3, finishing: 120 leaves an even surface, ready for painting or the next operation.
- Do not skip more than one step: jumping from 40 to 120, the fine disc struggles and wears needlessly.
- Change discs only once the scratches from the previous step have completely gone.
- Use an oscillating movement and change the angle, as Tyrolit recommends, and take regular breaks so the grinder does not overheat.
Flap disc safety
Never grind with the periphery of a flap disc: Tyrolit warns that the flaps can come off. Respect the maximum speed on the label, wear gloves when fitting fibreglass-backed discs, and use goggles, ear protection and a dust mask.
Why flap disc quality and markings matter
Two flap discs with the same grit can look identical yet perform very differently: the abrasive cloth, the number of flaps, their fixing and grain purity all matter. For the PREMIUM FASTCUT flap disc, Tyrolit states maximum stock removal and high grinding performance maintained over the whole disc life; on the PREMIUM LONGLIFE flap disc for steel, the diameter reduces during use, so 100% of the disc is used.
Grinding dust must not be inhaled, whatever the disc: Tyrolit requires extraction for dry operations and breathing apparatus in enclosed spaces. When grinding stone or concrete (for example with silicon carbide flap discs), the workpiece dust usually contains respirable crystalline silica. Directive (EU) 2017/2398 added “work involving exposure to respirable crystalline silica dust generated by a work process” to Annex I of Directive 2004/37/EC on carcinogens or mutagens at work and set a binding limit value of 0.1 mg/m³ (respirable fraction, 8-hour reference period). Use extraction and an FFP2 or FFP3 respirator.
Tyrolit flap discs made to EN 13743 vs unmarked discs
Tyrolit flap discs are made to EN 13743, the European standard for coated abrasives, and the label shows the standard, maximum speed, dimensions and manufacturer. Tyrolit is a founding member of oSa (Organisation for the Safety of Abrasives); according to Tyrolit, the oSa label guarantees compliance with EN safety standards, regular manufacturing controls and traceability to the manufacturer. With a disc that has no standard markings or identifiable manufacturer, you cannot know whether it is rated for your grinder’s speed, which grain it uses or how consistent its quality is between batches.
See also: Cheap vs premium discs
Frequently asked questions
What grit flap disc should I use for welds?
Start with 40 for large seams or 60 for moderate ones, smooth with 80 and, if needed, finish with 120. On stainless steel, choose zirconia (ZA) or ceramic (CA) grain.
What is the difference between 40 and 80 grit?
40 grit removes a lot of material quickly but leaves deep scratches. 80 grit removes less and leaves a finer surface, suitable for smoothing.
27A or 28A flap disc: which is better?
It depends on the job. The depressed-centre 27A works at 15–20° and is designed mainly for surfaces. The straight 28A works at 0–15° and is used on both edges and surfaces.
What does P40 or P80 mean on a flap disc?
The P prefix (P40, P80) refers to the FEPA scale for coated abrasives. Tyrolit catalogues print flap disc grits without it, after the grain type (ZA 40, ZA 60); the P in codes such as ZA-P43N denotes the PREMIUM line.
Can I use the same flap disc on steel and stainless steel?
Yes, if it is a 2in1 disc for steel and stainless steel, but use it on stainless first: a disc that has already been used on carbon steel should not go back onto stainless, as it can contaminate the surface with iron particles.
Find the right flap disc
Galflex is an authorized Tyrolit distributor in Romania. See the Tyrolit flap disc range or request an offer.
Sources and documentation
Related guides
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