An ISO carbide insert code such as CNMG 120408 is read one position at a time: C = 80° diamond shape, N = 0° clearance, M = tolerance class, G = hole with chipbreakers on both faces, 12 = 12 mm cutting edge (a 1/2 in inscribed circle), 04 = 4.76 mm thick and 08 = 0.8 mm nose radius. The same insert in the ANSI inch system is CNMG 432.
ISO 1832 gives every indexable turning and milling insert the same seven core positions: four letters (shape, clearance angle, tolerance, type) and three number groups (size, thickness, corner radius). Optional letters after the numbers describe the edge preparation and hand of cut, and anything after a dash (such as -PM or -MF) is the manufacturer's own chipbreaker code. Type a code into the decoder to see each position explained, or use the reference tables below. The ANSI (inch) system uses the same four letters but writes size in 1/8 in, thickness in 1/16 in and radius in 1/64 in.
Insert code decoder
The ISO 1832 positions at a glance
| Position | CNMG 120408 example | Meaning |
|---|---|---|
| 1 | C | Shape: 80° rhombic (diamond) |
| 2 | N | Clearance angle: 0° (negative insert) |
| 3 | M | Tolerance class: M (sintered to size, not ground) |
| 4 | G | Type: cylindrical hole, chipbreakers on both faces |
| 5 | 12 | Size: 12 mm cutting edge (12.9 mm), i.e. a 12.7 mm (1/2 in) inscribed circle |
| 6 | 04 | Thickness: 4.76 mm (3/16 in) |
| 7 | 08 | Corner (nose) radius: 0.8 mm (1/32 in) |
| 8, 9 (optional) | (none) | Edge condition and hand of cut, when given, e.g. E (honed) and R (right hand) |
| Suffix | -PM | Manufacturer chipbreaker / application code (not ISO) |
Position 1: insert shape
| Letter | Shape | Corner angle | Typical use |
|---|---|---|---|
| C | Rhombic (diamond) | 80° | General turning and facing; strong 80° corner. The most common turning insert. |
| D | Rhombic (diamond) | 55° | Profiling and copy turning; 55° point reaches into shoulders and undercuts. |
| S | Square | 90° | Roughing and chamfering; very strong 90° corner, 4 corners per side. |
| T | Triangle | 60° | General turning, facing and boring; 3 corners per side. |
| V | Rhombic (diamond) | 35° | Fine profiling and finishing; sharp 35° point for complex shapes, weakest corner. |
| W | Trigon (80° hexagon) | 80° | Turning and facing; 80° corners like C but 3 per side. |
| R | Round | none (round) | Profiling and heavy roughing; strongest edge, no corner. |
| A | Parallelogram | 85° | Mostly milling (e.g. APMT/APKT square-shoulder cutters). |
| K | Parallelogram | 55° | Some turning and grooving holders. |
| B | Parallelogram | 82° | Less common; special holders. |
| E | Rhombic (diamond) | 75° | Less common; special holders. |
| M | Rhombic (diamond) | 86° | Less common; special holders. |
| H | Hexagon | 120° | Less common; special holders. |
| O | Octagon | 135° | Face milling (octagon cutters). |
| P | Pentagon | 108° | Less common; special holders. |
| L | Rectangle | 90° | Less common; special holders. |
Smaller corner angles reach into tighter profiles but are weaker and run less feed; larger angles (and round inserts) are stronger and suit roughing.
Position 2: clearance (relief) angle
| Letter | Clearance angle |
|---|---|
| N | 0° |
| A | 3° |
| B | 5° |
| C | 7° |
| P | 11° |
| D | 15° |
| E | 20° |
| F | 25° |
| G | 30° |
| O | other (special) |
N (0°) marks a negative insert: its sides are square to the top face, so the holder tilts it to create clearance. Negative inserts are strong and, when they have chipbreakers on both faces (type G), can be flipped to use the corners on the underside too. Letters such as B (5°), C (7°) and P (11°) are positive inserts: one-sided, lighter cutting, better for small bores, slender parts and finishing.
Position 3: tolerance class
Three dimensions are toleranced: m (the corner height, measured from the corner to the inscribed circle), s (thickness) and d (inscribed circle). Values in mm; where a range is given, the tolerance grows with insert size.
| Class | m, corner (mm) | s, thickness (mm) | d, IC (mm) |
|---|---|---|---|
| A | ±0.005 | ±0.025 | ±0.025 |
| F | ±0.005 | ±0.025 | ±0.013 |
| C | ±0.013 | ±0.025 | ±0.025 |
| H | ±0.013 | ±0.025 | ±0.013 |
| E | ±0.025 | ±0.025 | ±0.025 |
| G | ±0.025 | ±0.13 | ±0.025 |
| J | ±0.005 | ±0.025 | ±0.05 to ±0.15 |
| K | ±0.013 | ±0.025 | ±0.05 to ±0.15 |
| L | ±0.025 | ±0.025 | ±0.05 to ±0.15 |
| M | ±0.08 to ±0.18 | ±0.13 | ±0.05 to ±0.15 |
| N | ±0.08 to ±0.18 | ±0.025 | ±0.05 to ±0.15 |
| U | ±0.13 to ±0.38 | ±0.13 | ±0.08 to ±0.25 |
M is the usual class for pressed-to-size (sintered) inserts; G and E are ground on the periphery for better repeatability when indexing. Ground inserts are sharper and more accurate but cost more.
Position 4: type (fixing hole and chipbreaker)
| Letter | Hole and chipbreaker |
|---|---|
| N | No hole, no chipbreaker |
| R | No hole, chipbreaker on one face |
| F | No hole, chipbreakers on both faces |
| A | Cylindrical hole, no chipbreaker |
| M | Cylindrical hole, chipbreaker on one face |
| G | Cylindrical hole, chipbreakers on both faces |
| W | Hole with 40–60° countersink on one face, no chipbreaker |
| T | Hole with 40–60° countersink on one face, chipbreaker on one face |
| Q | Hole with 40–60° countersink on both faces, no chipbreaker |
| U | Hole with 40–60° countersink on both faces, chipbreakers on both faces |
| B | Hole with 70–90° countersink on one face, no chipbreaker |
| H | Hole with 70–90° countersink on one face, chipbreaker on one face |
| C | Hole with 70–90° countersink on both faces, no chipbreaker |
| J | Hole with 70–90° countersink on both faces, chipbreakers on both faces |
| X | Special design (see the maker's drawing) |
A cylindrical hole (A, M, G) suits lever, pin or wedge clamping; a countersunk hole (T, W, Q, U and similar) is for a screw clamp, which is why most positive inserts like CCMT and DCMT are type T.
Position 5: size code (cutting edge length) by inscribed circle
The size number is the length of the cutting edge in mm with the decimals dropped. For each shape the same inscribed circle (IC) gives a different number, because the edge of a 35° diamond is much longer than the edge of a square. Round inserts (R) use the diameter in mm.
| IC (mm) | IC (in) | ANSI IC code | C 80° | D 55° | S 90° | T 60° | V 35° | W 80° | R |
|---|---|---|---|---|---|---|---|---|---|
| 3.97 | 5/32 in | 1.2 | 04 | 04 | 03 | 06 | 06 | – | 03 |
| 4.76 | 3/16 in | 1.5 | 04 | 05 | 04 | 08 | 08 | – | 04 |
| 5.56 | 7/32 in | 1.8 | 05 | 06 | 05 | 09 | 09 | – | 05 |
| 6.35 | 1/4 in | 2 | 06 | 07 | 06 | 11 | 11 | – | 06 |
| 7.94 | 5/16 in | 2.5 | 08 | 09 | 07 | 13 | 13 | – | 07 |
| 9.525 | 3/8 in | 3 | 09 | 11 | 09 | 16 | 16 | 06 | 09 |
| 12.7 | 1/2 in | 4 | 12 | 15 | 12 | 22 | 22 | 08 | 12 |
| 15.875 | 5/8 in | 5 | 16 | 19 | 15 | 27 | 27 | – | 15 |
| 19.05 | 3/4 in | 6 | 19 | 23 | 19 | 33 | 33 | – | 19 |
| 25.4 | 1 in | 8 | 25 | 31 | 25 | 44 | 44 | – | 25 |
Codes are calculated from ISO 1832 geometry (edge length = IC ÷ sin of the corner angle for diamonds, IC × √3 for triangles). Not every shape is made in every size; "–" means no trigon code is listed here for that IC. Many milling inserts (for example APMT 1604) are metric-sized parallelograms with no inch IC, so their number is simply the edge length.
Position 6: thickness
| ISO code | Thickness (mm) | Thickness (in) | ANSI code |
|---|---|---|---|
| 01 | 1.59 mm | 1/16 in | 1 |
| T1 | 1.98 mm | 5/64 in | 1.2 |
| 02 | 2.38 mm | 3/32 in | 1.5 |
| T2 | 2.78 mm | 7/64 in | 1.8 |
| 03 | 3.18 mm | 1/8 in | 2 |
| T3 | 3.97 mm | 5/32 in | 2.5 |
| 04 | 4.76 mm | 3/16 in | 3 |
| 05 | 5.56 mm | 7/32 in | 3.5 |
| 06 | 6.35 mm | 1/4 in | 4 |
| 07 | 7.94 mm | 5/16 in | 5 |
| 09 | 9.52 mm | 3/8 in | 6 |
The ISO code is the thickness in whole mm; a T in front of the digit marks the sizes in between (for example T3 = 3.97 mm, the 5/32 in thickness of a CCMT 09T304). ANSI codes count sixteenths of an inch, so ANSI 3 = 3/16 in = ISO 04.
Position 7: corner (nose) radius
| ISO code | Radius (mm) | Radius (in) | ANSI code |
|---|---|---|---|
| 00 | sharp | sharp | 0 |
| 01 | 0.1 mm | no inch equivalent | none |
| 02 | 0.2 mm | 1/128 | 0.5 |
| 04 | 0.4 mm | 1/64 | 1 |
| 08 | 0.8 mm | 1/32 | 2 |
| 12 | 1.2 mm | 3/64 | 3 |
| 16 | 1.6 mm | 1/16 | 4 |
| 20 | 2 mm | 5/64 | 5 |
| 24 | 2.4 mm | 3/32 | 6 |
| 32 | 3.2 mm | 1/8 | 8 |
The ISO code is the radius in tenths of a mm (08 = 0.8 mm). ANSI counts 64ths of an inch (2 = 2/64 = 1/32 in ≈ 0.79 mm), so the two systems match closely but not exactly. Round inserts use M0 (metric diameter) or 00 (inch diameter) here. Bigger radii give a stronger edge and better finish at a given feed but push the part harder; small radii suit slender parts and light depths of cut.
Positions 8 and 9, wiper facets and chipbreaker suffix
Position 8: edge condition
| Letter | Edge |
|---|---|
| F | Sharp edge |
| E | Rounded (honed) edge |
| T | Chamfered edge (T-land) |
| S | Chamfered and rounded edge |
| K | Double chamfered edge |
| P | Double chamfered and rounded edge |
Position 9: hand of cut
| Letter | Hand |
|---|---|
| R | Right hand |
| L | Left hand |
| N | Neutral (either hand) |
Wiper facet (milling, replaces position 7)
| 1st letter | Entering (lead) angle |
|---|---|
| A | 45° |
| D | 60° |
| E | 75° |
| F | 85° |
| P | 90° |
| Z | special |
The 2nd facet letter is the facet clearance angle, using the position 2 letters (D = 15°).
Manufacturer chipbreaker suffix: codes after the dash, such as -PM, -MF or -RP, are not covered by ISO 1832. Each maker uses its own letters; many start with the ISO material group (P steel, M stainless, K cast iron) followed by F, M or R for finishing, medium or roughing, but always check the maker's catalogue. The carbide grade (e.g. 4325, IC8250) is also a separate maker's code.
ANSI (inch) to ISO (metric) insert code conversion
The letters stay the same; only the numbers change. ANSI writes IC in 1/8 in, thickness in 1/16 in and radius in 1/64 in, so CNMG 432 = 4/8 in IC, 3/16 in thick, 2/64 in radius = CNMG 120408. Sizes under 1/4 in IC use decimal codes (1.2 = 5/32, 1.5 = 3/16, 1.8 = 7/32 in), and thickness codes such as 1.5 and 2.5 appear on small positive inserts, e.g. CCMT 32.51 = CCMT 09T304.
| ANSI (inch) code | ISO (metric) code |
|---|---|
| CNMG 431 | CNMG 120404 |
| CNMG 432 | CNMG 120408 |
| CNMG 433 | CNMG 120412 |
| CNMG 643 | CNMG 190612 |
| CNMG 644 | CNMG 190616 |
| DNMG 331 | DNMG 110404 |
| DNMG 431 | DNMG 150404 |
| DNMG 432 | DNMG 150408 |
| DNMG 441 | DNMG 150604 |
| DNMG 442 | DNMG 150608 |
| TNMG 331 | TNMG 160404 |
| TNMG 332 | TNMG 160408 |
| TNMG 333 | TNMG 160412 |
| TNMG 432 | TNMG 220408 |
| VNMG 331 | VNMG 160404 |
| VNMG 332 | VNMG 160408 |
| VBMT 331 | VBMT 160404 |
| VBMT 332 | VBMT 160408 |
| VCMT 331 | VCMT 160404 |
| WNMG 331 | WNMG 060404 |
| WNMG 332 | WNMG 060408 |
| WNMG 431 | WNMG 080404 |
| WNMG 432 | WNMG 080408 |
| WNMG 433 | WNMG 080412 |
| SNMG 432 | SNMG 120408 |
| SNMG 433 | SNMG 120412 |
| SNMG 543 | SNMG 150612 |
| SNMG 644 | SNMG 190616 |
| CCMT 21.51 | CCMT 060204 |
| CCMT 21.52 | CCMT 060208 |
| CCMT 32.51 | CCMT 09T304 |
| CCMT 32.52 | CCMT 09T308 |
| DCMT 21.51 | DCMT 070204 |
| DCMT 32.51 | DCMT 11T304 |
| DCMT 32.52 | DCMT 11T308 |
| TCMT 21.51 | TCMT 110204 |
| TCMT 21.52 | TCMT 110208 |
| TCMT 32.51 | TCMT 16T304 |
| SCMT 32.51 | SCMT 09T304 |
Worked examples
- DNMG 150608: 55° diamond, 0° clearance, class M, hole with chipbreakers both faces, 15 mm edge (12.7 mm IC), 6.35 mm (1/4 in) thick, 0.8 mm radius. ANSI DNMG 442.
- VBMT 160404: 35° diamond, 5° clearance (positive), class M, countersunk screw hole with chipbreaker on one face, 16 mm edge (9.525 mm IC), 4.76 mm thick, 0.4 mm radius. ANSI VBMT 331.
- CCMT 09T304: 80° diamond, 7° clearance, class M, screw hole with chipbreaker, 9 mm edge (9.525 mm IC), 3.97 mm thick, 0.4 mm radius. ANSI CCMT 32.51.
- APMT 1604PDER (milling): 85° parallelogram, 11° clearance, class M, screw hole with chipbreaker, 16 mm edge, thickness code 04, then PD = wiper facet for a 90° entering angle with 15° facet clearance, E = honed edge, R = right hand. It is metric-sized, so it has no ANSI equivalent.
Related calculators and charts
- Feed and Speed Calculator and Feeds and Speeds Sweet Spot Finder: cutting data for your insert.
- Surface Finish Predictor: finish from nose radius and feed.
- Chip Thinning Calculator: milling feed with a small radial engagement.
- Tool Life Estimator and Cutting Force Calculator.
- Center Drill Size Chart, G and M Code Reference and Tap & Drill Size Reference.
Frequently asked questions
Source: ISO 1832 (indexable inserts for cutting tools, designation) and the ANSI (inch) insert designation system. Size codes are calculated from the insert geometry; tolerance ranges are summarised. Chipbreaker and grade codes are manufacturer-specific. Always check critical values against the standard or the insert manufacturer's catalogue.