ISO 6106 Explained: What a Diamond Grit Number Actually Tells You

If a quotation for diamond powder gives you a mesh number and nothing else, it is not a specification. It is a label.

Mesh is a sieve, not a size

The old mesh system counts openings per inch on a woven screen. A powder “passing 325 mesh” means the particles went through a screen with 325 openings per inch. It says nothing about:

• the median particle size,
• how wide the distribution is,
• how many fine particles below the useful range are present,
• the shape of the particles.

Two powders both sold as 325 mesh can have medians of 35 and 48 microns, and behave entirely differently in a metal bond.

What ISO 6106 actually specifies

ISO 6106 (Diamond grit — designation and dimension) defines grit designations and the corresponding particle size distributions for superabrasive grit, measured by the electrical resistance zone method — a particle is sized by how much it disturbs an electric field as it falls through a sensing zone.

The result is reported as a distribution, not a single number:

The spread between D10 and D90 tells you how tight the classification is. Two powders with an identical D50 but a D90 differing by 40 percent will wear completely differently: the coarse tail dominates the cutting action and the fine tail fills the bond.

Why the coarse tail matters more than the median

In a metal bond saw segment, it is the largest particles that do the cutting. A powder with an aggressive coarse tail cuts faster and leaves a rougher finish; the same powder in a resin bond polishing wheel produces scratches that have to be removed downstream.

This is why buying on D50 alone is a trap. If a supplier quotes “D50 = 50 micron” and the D90 is 95 microns, you have bought a distribution, not a number, and you did not specify it.

The three readings to insist on

Before accepting a lot of diamond powder, ask for:

1. Laser diffraction or electrical zone PSD with D10, D50 and D90, against the standard you agreed. One number is not a report.
2. A morphology photo at SEM, or at minimum a high-magnification optical image, showing whether particles are blocky, needle-like or irregular, and whether any coating is intact and continuous.
3. Impact toughness / friability, if the application is a saw segment or a metal bond wheel. Toughness decides whether grit fractures progressively, which is what keeps a cutting edge sharp, or shatters.

For resin bond and electroplated products, add impurity checks for graphitic carbon and metallic contamination — both cause localised soft spots that show up much later as uneven wheel wear.

What changes when you buy direct

The reason to buy diamond powder factory-direct is not only price. It is that a factory that synthesises its own grit can select a distribution, whereas a trader can only sell you what is on the shelf.

If your process is sensitive to the coarse tail — and most precision grinding and most resin bond work is — that selection is worth more than the percentage you save on the invoice.

Related reading

• diamond micro powder, factory direct
• what D50 hides about a powder lot
• how we verify a powder certificate

Specifying diamond powder and unsure whether a certificate is tight enough? Send it to us — we will tell you what is missing and what it will cost to hold.