Carbide Insert Grades Explained
An insert's ISO code (like CNMG 120408) describes its shape and size — it says nothing about what the cutting edge itself is made of. That's the insert's "grade": the carbide substrate composition and any coating applied to it, which together determine how the insert holds up against a specific material and cutting condition.
The ISO material groups (P / M / K / N / S / H)
ISO 513 defines six colour-coded material groups that grades are built around: P (blue) for steel, M (yellow) for stainless steel, K (red) for cast iron, N (green) for non-ferrous metals like aluminium, S (brown) for superalloys and titanium, and H (grey) for hardened steels. A grade optimised for one group will generally underperform, or wear unpredictably, on a material from a different group — which is why the same insert shape is often sold in several different grades.
Coated vs uncoated
Most grades for steel, stainless steel and cast iron carry a CVD or PVD coating, which adds wear resistance and heat resistance at the cost of a slightly less sharp edge. Grades for aluminium and other non-ferrous work are frequently uncoated and polished instead, since a sharp edge matters more than heat resistance for these materials, and coatings can actually encourage material to stick to the edge.
Why we don't quote a single "best grade"
Grade naming and exact composition are brand-specific, and the right choice depends on your material, cutting speed, coolant use and whether the cut is continuous or interrupted. This is exactly the kind of detail we ask for rather than guess at — telling us your material and operation lets us point you to a suitable equivalent, rather than publishing a generic recommendation that might be wrong for your specific job.
How to tell us what you need
If you already have a grade in use, share the brand and grade name and we'll help identify the closest equivalent available through us. If you're starting fresh, tell us the material, operation (roughing or finishing) and whether the cut is continuous or interrupted.