How to Read ISO 车削刀片 Codes: CNMG, WNMG, CCMT and More

Decode insert shape, clearance, tolerance, mounting style and size using three common turning examples. Learn which parts of a full model remain brand-specific.

An ISO insert designation tells you the basic geometry of an indexable insert. It does not, by itself, tell you that two brands use the same grade, chipbreaker, coating or cutting data. Read the standard designation first; then check the full manufacturer model and the holder seat before ordering.

The seven positions in the basic designation

Under ISO 1832, the familiar four letters and following size characters are read in order. The numbers are designation codes, not a promise that each printed number equals a dimension in millimetres. Confirm the actual dimensions from the manufacturer’s drawing.

Position	What it describes	What to check
1 — Shape	The insert outline, such as C (80° rhombic) or W (80° trigon).	Shape and seat must match the toolholder.
2 — Clearance	The normal relief angle. N denotes 0°; C denotes 7°.	Do not confuse clearance with the working rake angle created by the holder and chipbreaker.
3 — Tolerance	The dimensional tolerance class, such as M.	The class is not a carbide grade or workpiece material.
4 — Insert type	The hole and chipbreaker arrangement. G and T identify different mounting/face arrangements.	Check the maker’s drawing for the exact hole and seating geometry.
5 — Size	A nominal size code interpreted together with the shape.	For these examples, CNMG 12 and WNMG 08 can both have a 12.70 mm inscribed circle.
6 — 厚度	A thickness code, such as 04 or T3.	Examples below use 04 = 4.76 mm and T3 = 3.97 mm; verify the actual item.
7 — Corner radius	The nose-radius code. In the examples below, 08 = 0.8 mm and 04 = 0.4 mm.	Changing radius can change the finish, edge strength and programming offset.

Read three common models, one position at a time

CNMG 120408

C is an 80° rhombic shape; N is 0° normal clearance; M is the tolerance class; G specifies a cylindrical fixing hole and chipbreaker features on both faces in this designation. The 12 size corresponds to a 12.70 mm inscribed circle in the catalogued example. 04 denotes 4.76 mm thickness, and the final 08 denotes a 0.8 mm nose radius.

CNMG is a common negative-clearance, double-sided insert format for general turning. The complete saleable SKU still needs the maker’s chipbreaker and grade designation; “CNMG 120408” alone is not enough to choose an exact cutting edge.

WNMG 080408

W is an 80° trigon; N is 0° normal clearance; M is the tolerance class; G denotes the cylindrical hole and double-face chipbreaker arrangement. For this W shape, size code 08 corresponds to a 12.70 mm inscribed circle in the catalogued example—another reason not to treat the printed size code as a direct millimetre measurement. 04 denotes 4.76 mm thickness; the final 08 is a 0.8 mm nose radius.

The W outline offers three corners on each face in the usual double-sided format. It is not interchangeable with a CNMG insert merely because both examples have the same inscribed-circle diameter; the seat geometry differs.

CCMT 09T304

C is an 80° rhombic shape; the second C denotes 7° normal clearance; M is the tolerance class; T specifies a countersunk fixing-hole arrangement with chipbreaker features on one face. Size 09 corresponds to a 9.52 mm inscribed circle in the catalogued example. T3 denotes 3.97 mm thickness and the final 04 denotes a 0.4 mm nose radius.

CCMT is a positive-clearance insert format. 对比d with the zero-clearance examples above, the insert and holder combination may be useful where a lighter cutting action is needed. Confirm holder compatibility and choose a manufacturer-specific geometry for the actual cut.

CNMG vs WNMG vs CCMT: where to start

Family	Basic geometry	Practical starting point
CNMG	80° rhombic, 0° normal clearance, commonly double-sided.	General turning where the holder and workpiece clearance suit this shape.
WNMG	80° trigon, 0° normal clearance, commonly double-sided.	General turning when a W-style seat and its available corners suit the job.
CCMT	80° rhombic, 7° normal clearance, one-face T-type configuration.	Lighter-cutting or internal-turning setups where a compatible positive-clearance insert is specified.

These are starting points, not a ranking. The holder, approach angle, available clearance, workpiece material and machining stage all matter. A grade or chipbreaker code such as a maker’s finishing or medium geometry is not standardised across brands by the seven-position ISO designation.

What to confirm before ordering

Record the complete model printed on the pack or insert, including any suffix and grade.
Check shape, clearance, size, thickness, radius and fixing hole against the toolholder’s insert specification.
Specify the workpiece material and whether the cut is finishing, medium or roughing.
对比 the brand’s available chipbreakers and grades for those conditions.
If replacing another brand, send the current model or a clear photo rather than assuming that similar letters mean a direct substitute.

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Technical references

ISO 1832:2017 — Indexable 刀片 for cutting tools — Designation; Sandvik Coromant catalogue dimensions for CNMG and CCMT examples; Sandvik Coromant catalogue dimensions for WNMG examples. Check the current manufacturer’s product sheet for the item you intend to order.