Abrasive grit guide: choosing grinding wheels, flap discs and sandpaper
Last updated 2026-11-09
The grit number is the size of the abrasive particles: the lower the number, the coarser the grit and the faster it removes material. Start coarse enough to do the job quickly, then step up to finer grits to smooth out the scratches.
Grit numbers at a glance
| Grit | Grade | Typical use |
|---|---|---|
| 24–36 | Extra coarse | Heavy stock removal, grinding down welds, stripping heavy rust and paint |
| 40–60 | Coarse | General grinding and blending, weld cleanup, shaping |
| 80–120 | Medium | Blending, removing coarse scratches, surface prep before painting |
| 150–240 | Fine | Finishing, light deburring, sanding between coats |
| 320 and up | Very fine | Polishing and final finishing |
A good rule: don't skip more than one grit step at a time (for example 40 → 60 → 80 → 120), or the coarser scratches won't come out.
Flap discs: Type 27 vs Type 29
- Type 27 (flat): for flat surfaces and blending. Hold the grinder at a low angle (roughly 0–15°).
- Type 29 (conical): angled flaps for faster stock removal on edges and contours. Hold at a steeper angle (roughly 15–25°).
Flap discs grind and finish in one step and run cooler than a hard grinding wheel. Shop flap and fiber discs.
Abrasive grains compared
- Aluminum oxide: the economical general-purpose grain for steel and wood.
- Zirconia alumina: tougher and longer-lasting on steel and stainless; a good choice for weld grinding.
- Ceramic: the fastest-cutting and longest-lasting on hard metals and stainless under heavy pressure; costs more per disc but often less per job.
- Silicon carbide: sharp and fast on non-ferrous metals, stone, glass and finishing work.
Cut-off and grinding wheel safety
- Match the RPM: the wheel's maximum RPM must be at or above the grinder's rated speed.
- Cut-off wheels cut; they don't side-grind. Thin cut-off wheels (Type 1 and Type 27 cut-off) are not made for pressure on their face. Use a grinding wheel or flap disc for grinding.
- Keep the guard on and wear eye and face protection. See eye and face protection.
- Inspect wheels before use and throw out any that are cracked, chipped or have been dropped.
Shop grinding and cut-off wheels, sanding belts, sheets and pads and wire brushes and wheels.
Common questions
What grit flap disc should I use to grind welds?
Start with 40 or 60 grit to take the weld down quickly, then finish with 80 or 120 grit to blend it into the surrounding metal.
What does a higher grit number mean?
A higher number means finer particles: slower removal and a smoother finish. A lower number means coarser particles and faster removal.
Can I grind with a cut-off wheel?
No. Cut-off wheels are thin and built for cutting with pressure on their edge. Side pressure can break them. Use a grinding wheel or flap disc for grinding.
Need help?
Tell us the material and the finish you need and we'll recommend a grit and grain: call (908) 824-0916 or send us a message.