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CNMG Inserts — Code, Grades & Real Prices

What CNMG actually stands for

Four letters and six digits, and every one of them is a decision you are making. Here is the full decode — not just for CNMG but for any ISO turning insert:

The first four letters and the six digits are standardised by ISO 1832. Everything after that is the manufacturer’s own business — which is why two inserts with identical first ten characters can behave completely differently.

Worked example: CNMG 432 is the same insert as CNMG 120408

This trips people up constantly, and it causes real ordering errors. The inch and metric designations describe the same insert in two different numbering systems.

So when a supplier offers you “CNMG 120408” against your drawing that says “CNMG 432”, they are the same insert. When they offer CNMG 431 or 433 instead, the corner radius has changed — 431 is a sharper 1/64″ corner for finishing, 433 a sturdier 3/64″ for roughing — and that will show up in the surface finish or in edge chipping.

The third letter is where money is quietly lost. An M-class insert and a G-class insert of the same size differ by whether the cutting tip is held to the inscribed circle to ±0.002–0.005″ or to ±0.001″. On a finishing operation that difference is the whole tolerance budget. On a roughing operation you are paying for precision the part never sees.

When we quote, we ask which class your drawing actually needs — because G class costs more, and on most roughing work it buys nothing.

Choosing the grade for a CNMG insert

Cutting speeds for a CNMG insert

Typical starting windows for a CVD-coated CNMG insert in the P20–P35 / M10–M30 class, wet:

Wide bands on purpose. The right point inside the band depends on depth of cut, whether the cut is interrupted, coolant delivery and how rigid the setup is. Start in the middle and move in the direction that suits the failure you are seeing — if the edge is wearing, come up in speed; if it is chipping, come down and check the setup.

What CNMG inserts actually cost

Most pages on this subject show you a US or European distributor price and call it market price. Those are two different numbers. Here is the range for material actually leaving a Chinese factory:

What this table is and is not. These are ranges we observed across Chinese factory listings in September 2026 for standard CNMG 432 inserts in common coated grades, at the quantities shown. They are not a quotation and they are not our prices. Price moves with grade, coating type and thickness, tolerance class, chipbreaker complexity and order quantity — a CBN or wiper version sits well outside the range above. We publish the range because a buyer who does not know the floor cannot tell whether a quote is good.

What a complete insert quotation has to contain

A price on its own tells you nothing about what will arrive. We will not send one. Every quotation we issue states:

• The grade, written as a composition — not just “P25” but the cobalt content and grain size the plant will actually deliver.
• The coating — type, process and target thickness in micrometres.
• The chipbreaker — identified by the manufacturer’s own code, plus its feed and depth-of-cut window.
• The tolerance class — because this is the line item that decides whether the insert fits your finishing operation.
• Lead time for the actual quantity, not a stock figure that does not apply to your grade.
• A stated rejection policy — what happens, and who pays, if the batch fails incoming inspection.

If a quotation you receive is missing three of those six, you are comparing a number against a number, and the cheaper one will usually be the one that was not fully specified.