Flap Disc Grit Guide: 36, 40, 60, 80 & 120
The right flap disc grit determines how quickly you remove metal and how much finishing work remains. This flap disc grit guide compares 36, 40, 60, 80 and 120 grit for weld removal, deburring, surface blending and finishing preparation on steel and stainless steel.
Quick answer: which flap disc grit should you choose?
36 grit is for heavy removal, 40 grit for aggressive weld cleanup, 60 grit for general grinding and blending, 80 grit for controlled preparation, and 120 grit for finer blending before the next finishing step.
That is a starting point, not a universal finish guarantee. Abrasive grain, disc shape, pressure, grinder speed, metal and the previous scratch pattern all affect the result.
Flap disc grit chart
| Grit | Relative action | Practical starting uses | Watch for |
|---|---|---|---|
| 36 | Extra coarse | Heavy stock removal, proud welds, scale and rough edge work | Deep scratches, heat and accidental gouging on thin material |
| 40 | Coarse | Aggressive weld cleanup and fast grinding with slightly more control than 36 | Still too coarse when the final appearance is important |
| 60 | Coarse / general purpose | Weld blending, deburring and general fabrication cleanup | May not erase every 36-grit scratch in one pass |
| 80 | Medium | Controlled surface preparation, smoothing and blending before finishing | Slower removal on heavy welds and thick scale |
| 120 | Fine | Finer blending, scratch refinement and preparation for a subsequent finish | Loading, glazing or wasted time when used for heavy removal |
Catalog check: Machinist's Vault standard Type 27 zirconia discs are offered in 40, 60, 80 and 120 grit. Premium Type 27 and Type 29 zirconia discs add a 36-grit option. Select the grit and pack size on the product page.
What the grit number actually means
A lower grit number identifies a coarser abrasive size. The larger cutting points remove material quickly and leave a more pronounced scratch pattern. A higher number uses finer abrasive and usually cuts more slowly while producing a more controlled surface.
Grit is only one part of performance. A premium zirconia disc can maintain useful cutting action longer under production pressure than an unsuitable abrasive, and a Type 29 profile concentrates contact differently from a Type 27 disc. Compare shape in our Type 27 vs. Type 29 flap disc guide.
How to choose between 36, 40, 60, 80 and 120 grit
Plan the abrasive sequence from the final surface backward
If the part only needs functional deburring, one 60- or 80-grit step may be enough. If a visible weld must disappear into a flat surface, use the coarsest grit that removes it without gouging, then refine the scratch pattern.
- Heavy weld to blended surface: 36 or 40 grit, followed by 60 or 80.
- Moderate cleanup: 60 grit, followed by 80 or 120 when needed.
- Light oxidation or coating preparation: 80 or 120 grit after confirming the coating manufacturer's surface requirements.
Do not assume every grit jump is acceptable. Test on scrap or a hidden area, especially on appearance-critical stainless and thin sheet.
Match grit to disc shape, pressure and material
Use a Type 27 flap disc at the shallow working angle specified by its manufacturer for flat work and broad blending. Use Type 29 when the conical profile and steeper working angle suit welds, edges and concentrated removal. Do not force either profile flat or exceed its marked maximum speed.
Excessive pressure does not turn a fine disc into a coarse disc. It can add heat, reduce control and accelerate wear. If removal is too slow, stop and choose an appropriate coarser grit or higher-performance abrasive rather than leaning harder on the grinder.
For stainless steel, use a disc approved for stainless and keep it dedicated to stainless work when contamination control matters. For aluminum and non-ferrous metals, choose an abrasive specifically recommended for that material and confirm loading behaviour.
Recommended flap discs by grit and shape
All three choices are 4-1/2 × 7/8 inch zirconia flap discs made in Canada and rated to a maximum 13,300 RPM. Verify grinder compatibility and select the required grit and pack size.
Standard Zirconia Type 27
Flat-profile value for regular fabrication work in 40, 60, 80 and 120 grit.
Premium Zirconia Type 27
Flat-profile production line with 36, 40, 60, 80 and 120 grit options.
Premium Zirconia Type 29
Conical profile for concentrated contact, also offered from 36 through 120 grit.
Flap disc grit FAQ
What flap disc grit is best for removing welds?
Use 36 grit for the fastest heavy removal when the disc is offered in that grit, or 40 grit for aggressive weld cleanup with slightly more control. Switch to 60 or 80 grit when the weld is close to flush and the surrounding surface must be blended.
Is 40 grit or 60 grit better for a flap disc?
Choose 40 grit when removal speed matters most. Choose 60 grit for a more balanced cut and finish during general grinding, deburring and blending.
What is 80 grit used for on metal?
An 80-grit flap disc is a practical choice for controlled surface preparation, smoothing scratches left by coarser abrasives and blending before a finer finishing step.
Can a 120-grit flap disc polish metal?
A 120-grit flap disc can produce a finer blended surface, but it is not a polishing wheel. The final appearance depends on the metal, abrasive grain, pressure, previous scratch pattern and any finishing steps that follow.
Should I skip grits when blending metal?
You can sometimes move directly from a coarse grit to a fine grit, but a large jump may leave deep scratches visible. On appearance-critical work, test a two-step sequence such as 40 to 80 or 60 to 120.
Does flap disc shape change which grit I should use?
Yes. A Type 27 flat disc spreads contact across flatter work, while a Type 29 conical disc concentrates contact at a steeper angle. The same grit can feel more or less aggressive depending on disc shape, pressure and the workpiece.
Can I use the same flap disc on steel and stainless steel?
Only when the disc is specified for both materials. To reduce iron contamination on stainless steel, keep abrasives dedicated to stainless work and follow your shop's contamination-control procedure.
Safety and technical references
Inspect the disc before mounting, use the correct guard and backing hardware, verify that the disc's maximum RPM is at least the grinder's no-load speed, and wear the PPE required by your workplace assessment and product instructions. References: Norton grit guide, Norton flap disc safety guidance, 3M flap disc range and the OSHA grinder checklist.
Continue learning: compare Type 27 and Type 29 flap disc profiles, or visit the Machinist's Vault Education hub.
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Reviewed By
This guide is reviewed by Kartar Chalotra, who leads sales and operations at Rise Tek Machinery.