Choosing the Right Grit for Plain File Board Sheets
By Supergrit Abrasives | Published: 2026-10-19
Category: Buying Guides
Learn how to select the best grit for plain file board sheets based on your material and finish goals. Compare aluminum oxide vs. zirconia options.
Quick answer
For rough material removal on metal or wood, start with a coarse grit (36–80). For finishing or light deburring, use a finer grit (120–220). Choose aluminum oxide for general-purpose work and zirconia for high-pressure grinding on metal.
Why grit choice matters for file board sheets
Plain file board sheets are versatile because they fit standard file holders and allow you to match the abrasive to the task. The grit number directly affects how fast you remove material and how smooth the surface ends up. Using the wrong grit can waste time or leave scratches that are hard to fix.
Aluminum oxide vs. zirconia: what each does best
Aluminum oxide (AO) is the traditional choice for wood, paint, and softer metals. It fractures to expose fresh sharp edges, so it works well on a wide range of surfaces. Zirconia abrasive is tougher and stays sharp longer under high pressure, making it a better fit for heavy grinding on stainless steel or hard alloys. The trade-off is cost: zirconia sheets cost more per pack, but they last longer on demanding jobs.
Decision rules for picking the right grit
- Coarse grits (36–80): Use for rapid stock removal, shaping edges, or removing heavy rust and weld beads. Grit 36 or 40 cuts aggressively; grit 80 leaves a rough surface ready for finer sanding. Start with the coarsest grit that removes material fast enough—going too fine first wastes time.
- Medium grits (100–150): Ideal for smoothing surfaces after coarse work, deburring machined parts, or blending scratches on wood and metal. Grit 120 is a common all-purpose starting point for finishing.
- Fine grits (180–220): Best for final finishing, light polishing, or cleaning up before painting or coating. Grit 220 produces a smooth surface that minimizes visible scratches. If you need a mirror finish, plan to switch to even finer abrasives (320+) after the file board step.
- Material match: On wood, aluminum oxide works well across all grits. On stainless steel or hard alloys, zirconia in coarse or medium grits extends sheet life and cuts faster under pressure. For mixed-material projects, keep both AO and zirconia sheets on hand and swap based on the specific job.
Product facts at a glance
- 2 3/4" X 17 1/2" PLAIN MIRKA GOLD AO FILE BOARD SHEETS: Mirka Gold AO file board sheets are plain sheets sized 2 3/4 x 17 1/2 inches, offered in grits from 36 to 220 in packs of 50. The wide grit range lets you use the same sheet format for everything from aggressive shaping to fine finishing, and the pack of 50 keeps you stocked for multiple projects.
2 3/4" X 17 1/2" PLAIN MIRKA GOLD AO FILE BOARD SHEETS - 2 3/4" X 17 1/2" PLAIN ZIRCONIA FILE BOARD SHEETS: Supergrit Abrasives plain zirconia file board sheets are the same size and come in grits 36 to 180F, sold in packs of 50. Zirconia construction handles higher pressure and resists dulling on metal, so you get longer use per sheet when grinding or deburring hard materials.
2 3/4" X 17 1/2" PLAIN ZIRCONIA FILE BOARD SHEETS
Who should use each type
Best for
- DIYers and woodworkers who need a versatile, cost-effective abrasive for shaping and finishing wood or paint
- Metalworkers grinding stainless steel or hard alloys who want longer sheet life under high pressure
Not ideal for
- Tasks requiring wet sanding or extremely fine finishes (above 400 grit) – file board sheets top out at 220 grit
