Short answer: a bonded abrasive specification reads left to right as abrasive grain → grit size → grade (hardness) → bond → shape type. In A 30 S BF 27, that is aluminium oxide, grit 30, grade S, resinoid bond with fibreglass reinforcement, shape Type 27.
The specification code
| Position | Example | Meaning |
|---|---|---|
| Abrasive | `A` | Type of grain |
| Grit size | `30` | Coarseness |
| Grade | `S` | Hardness of the bond |
| Structure | `7` | Grain spacing (often omitted on resinoid wheels) |
| Bond | `BF` | Bonding system |
| Shape | `27` | Geometry / shape type |
Abrasive grain
| Code | Abrasive | Best suited to |
|---|---|---|
| A | Aluminium oxide | Carbon and alloy steel, general fabrication |
| WA | White aluminium oxide | Heat-sensitive steels, cooler cutting |
| Z / ZA | Zirconia alumina | High-pressure stock removal, tough steels |
| C | Silicon carbide | Cast iron, non-ferrous metals, stone, concrete, glass |
| NQ / SG | Ceramic | High-performance production grinding |
Zirconia and ceramic grains are tougher and self-sharpen under pressure, which is why they last longer in aggressive stock removal. See Zirconia vs Aluminum Oxide.
Silicon carbide is the family used for non-metallics — it is why Glass Grinding Wheels use a different grain from steel wheels.
Grit size
Lower numbers are coarser and cut faster; higher numbers are finer and leave a better surface.
- Coarse: 16, 20, 24 — heavy stock removal
- Medium: 30, 36, 46, 60 — general grinding and cutting
- Fine: 80 and above — finishing and blending
Grade (hardness)
Grade describes how firmly the bond grips the grain, not how hard the abrasive is. Letters run from soft to hard:
- Soft: N, O, P — the bond releases dull grains readily, exposing fresh ones
- Medium: Q, R, S — general purpose
- Hard: T, U, V — the bond holds grains longer, so the wheel lasts longer but can glaze
The counter-intuitive rule: use a softer grade on hard materials, and a harder grade on soft materials. A hard wheel on hard steel holds onto dull grain and stops cutting — that is glazing. See How to Prevent Wheel Glazing.
Structure
A number, roughly 1–15, describing how densely grains are packed. Lower is denser. Vitrified wheels usually show it; thin resinoid cutting wheels often omit it.
Bond
| Code | Bond | Notes |
|---|---|---|
| V | Vitrified | Rigid, glass-like. Bench and precision wheels |
| B | Resinoid (bakelite) | Tougher, tolerates side load better than vitrified |
| BF | Resinoid + fibreglass reinforcement | Standard for hand-held cutting and grinding wheels |
The F is the safety-critical part. Fibreglass mesh holds a wheel together if it starts to fail, which is why virtually every portable cut-off and depressed-centre wheel is BF.
Shape type
| Type | Geometry | Application |
|---|---|---|
| 27 | Depressed centre, flat face | Grinding |
| 28 | Depressed centre, saucer profile | Grinding |
| 41 | Flat, straight | Cutting-off |
| 42 | Depressed centre | Cutting-off |
Types 27, 28, 41 and 42 are the shapes normally found on hand-held machines. For the practical difference see Grinding Wheel vs Cutting Wheel and Type 27 vs Type 28 Grinding Wheels.
The safety markings EN 12413 requires
Separately from the specification code, a compliant wheel carries information that exists purely for safety. Look for:
- Dimensions as diameter x thickness x bore, e.g.
230 x 3 x 22.23 - Maximum operating speed in m/s, and usually the matching rpm
- Shape type
- Restriction and warning pictograms — eye protection, guard required, and any "not for hand-held use" or "not for side grinding" symbols
- Expiry date for resin-bonded products
- Manufacturer identification
If any of this is missing or illegible, treat the wheel as unusable. The markings are the only record of what the wheel was tested to do. More detail in Understanding EN 12413 Safety Standards.
Reading a full marking in practice
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Type 41 - 230 x 3.0 x 22.23 - A 30 S BF - 80 m/s (6600 rpm)
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- Type 41 — flat cutting-off wheel, not for side grinding
- 230 x 3.0 x 22.23 — 230 mm diameter, 3 mm thick, 22.23 mm bore
- A 30 S BF — aluminium oxide, grit 30, medium grade, reinforced resinoid
- 80 m/s (6600 rpm) — do not fit to a machine whose no-load speed exceeds 6,600 rpm
That is enough to decide, in seconds, whether the wheel suits the job and the machine. Verify the speed logic with Abrasive Wheel Speed: How to Check RPM and Peripheral Speed.
Frequently asked questions
What does A30SBF mean on a grinding wheel?
Aluminium oxide grain, grit 30, grade S (medium hardness), resinoid bond with fibreglass reinforcement.
Which letter is the hardness in a wheel spec?
The single letter after the grit number. N–P soft, Q–S medium, T–V hard.
Does a harder wheel last longer?
It holds grain longer, but on hard material it glazes and stops cutting. Match grade to material rather than chasing wheel life.
What is the difference between B and BF bond?
Both are resinoid. BF adds fibreglass reinforcement and is the norm for portable cutting and grinding wheels.
What do the numbers 230 x 3 x 22.23 mean?
Outside diameter x thickness x bore, all in millimetres.
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