What does CNMG090308 mean? Every position of the ISO 1832 code, decoded
CNMG090308 is not a part number, it is a sentence. Four letters describe the insert — shape, clearance, tolerance, fixing and chipbreaker — and the number block 090308 gives its size, thickness and nose radius. Decoded below, position by position.
- C — shape
- 80° rhombic (diamond) · the general-turning workhorse: one insert turns and faces, with a corner strong enough for most first-choice work
- N — clearance angle
- relief angle 0° (negative insert, double-sided use possible)
- M — tolerance
- class M — molded, medium tolerance on inscribed circle and corner point (typically ±0.05–0.13 mm depending on size)
- G — type
- cylindrical fixing hole, chipbreaker on both faces (double-sided insert)
- 09 — size
- size class 9 — nominal cutting-edge length class in mm; the exact edge length and inscribed circle depend on the shape, see a catalog drawing
- 03 — thickness
- insert thickness 3.18 mm
- 08 — corner radius
- Rε = 0.8 mm nose radius
| Shape | 80° rhombic (diamond) |
| Insert style | Negative, double-sided |
| Usable edges | 4 (typical, 2 corners × 2 faces) |
| Thickness | 3.18 mm |
| Nose radius | 0.8 mm |
| Size class | 9 (nominal cutting-edge length class, mm — exact dimensions depend on shape) |
Negative or positive — what position 2 commits you to
The N in position 2 means 0° clearance: a negative insert. Combined with the G type it is double-sided, so both faces carry cutting corners — 4 usable edges per insert. Negative inserts are the strongest option but push harder into the cut; the holder tilts them to create clearance.
The 0.8 mm nose radius in practice
The final 08 is the nose radius in hundredths of a millimetre: 0.8 mm — the general-purpose radius: a balance of corner strength and achievable finish that suits most first-choice turning. Surface roughness scales with feed² over radius, so radius choice sets your feed ceiling for a given finish.
One honest caveat: this page decodes the geometry. Which carbide grade, coating and chipbreaker to run on it is a separate decision that depends on your material and cut — the code alone cannot answer it. Dimensions here are nominal ISO classes; verify exact edge length against a maker's catalog drawing.
Same family, cross-referenced CNMG120404 · CNMG120408 · CNMG120412
| CNMG090308 (ISO 1832) | = CNMG 322 (ANSI B212.4) |
| Same insert geometry, two designation systems: the ANSI size digit is the inscribed circle in eighths of an inch, thickness in sixteenths, nose radius in sixty-fourths. US catalogs and forums use the inch code. | |