A code like CNMG 120408 is not random. Each position names one thing: shape, clearance, tolerance, chipbreaker and fixing, size, thickness and nose radius. Paste a code into the live decoder below, or learn the seven positions once and read any insert in the drawer, brand-neutral.
Instant, brand-neutral, and private: it runs entirely in your browser and nothing is sent anywhere. Decodes the ISO 1832 turning-insert designation system.
Take CNMG 120408 apart one position at a time. The first four are letters that describe the insert, the last block of numbers is its size.
| Pos | Symbol | What it defines | In CNMG 120408 |
|---|---|---|---|
| 1 | C | Insert shape, set by the corner angle | 80° rhombic (diamond), the general-turning workhorse |
| 2 | N | Clearance (relief) angle | 0°, so it is a negative, double-sided insert |
| 3 | M | Tolerance class on size and thickness | Medium, general purpose |
| 4 | G | Type: fixing hole and chipbreaker | Hole plus chipbreaker on both faces |
| 5 | 12 | Cutting edge length (size) | 12 size, a ½ inch / 12.7 mm inscribed-circle class |
| 6 | 04 | Thickness | 4.76 mm (3/16 in) |
| 7 | 08 | Nose (corner) radius | 0.8 mm |
ISO 1832 turning insert designation. The same logic underlies the ANSI B212 code, with minor differences in the number block.
The first letter is the corner angle. Bigger angle means a stronger corner and more heat capacity but worse access into a profile. Smaller angle reaches into tight features but the tip is fragile.
| Letter | Shape | Corner angle | Where it earns its place |
|---|---|---|---|
| R | Round | no corner | Heaviest roughing, strongest edge, high feed |
| S | Square | 90° | Strong edge for facing and roughing where access allows |
| C | Rhombic | 80° | The workhorse: turning and facing with one insert |
| W | Trigon | 80° | Three strong 80° corners, single-sided, turning and facing |
| T | Triangle | 60° | Versatile, more corners, good with decent access |
| D | Rhombic | 55° | Profiling, more side clearance than a C |
| V | Rhombic | 35° | Fine profiling and tight detail, weakest tip |
The second letter is the clearance angle, and it quietly dictates your holder and your cutting forces before you look at anything else.
N (0°) is a negative insert: double-sided, so twice the edges, the strongest option, but it pushes harder into the cut and needs a holder that tilts it to create clearance. C (7°), P (11°) and friends are positive: single-sided, lower cutting forces, kinder to thin walls, small machines and gummy material. Position 2 tells you whether you are holding a roughing tank or a finishing scalpel.
| Letter | Clearance | Insert character |
|---|---|---|
| N | 0° | Negative, double-sided, strongest, highest forces |
| A | 3° | Positive, low clearance |
| B | 5° | Positive |
| C | 7° | Positive, common general clearance |
| P | 11° | Positive, common in finishing geometries |
| D | 15° | High positive, light cuts |
| E | 20° | High positive, soft and sticky materials |
The third letter is how tightly the insert is held to size on the inscribed circle, thickness and corner.
| Class | Character | Use |
|---|---|---|
| G | Precision, ground | Tight tolerance, finishing and fixed-pocket tools |
| M | Medium | The default for general turning, pressed and sintered |
| U | Utility | Looser, as-pressed, economical roughing |
The fourth letter pairs how the insert clamps with whether it has a moulded chipbreaker. It is why a CNMG and a CNGG behave nothing alike on the same part.
| Letter | Fixing hole | Chipbreaker |
|---|---|---|
| A | Yes | None |
| M | Yes | One side |
| G | Yes | Both sides (so it suits double-sided negative inserts) |
| N | No | None |
| R | No | One side |
The number block is dimensional. Read it as three pairs: size, thickness, then nose radius.
| Block | Meaning | How to read it |
|---|---|---|
| 12 | Cutting edge length (size) | Nominal edge length in mm. 12 is the ½ inch / 12.7 mm inscribed-circle class. Bigger number, bigger insert and deeper cut. |
| 04 | Thickness | 4.76 mm (3/16 in). Thicker resists bending and breakage under heavy feed. |
| 08 | Nose radius | Hundredths of a mm: 08 = 0.8 mm. 04 = 0.4 mm, 12 = 1.2 mm, 16 = 1.6 mm. |
A bigger nose radius gives a stronger corner and a better finish at higher feed, because surface roughness scales with feed squared over radius. The cost is higher radial force and more chatter risk on thin or overhung parts. When a slender part rings, a smaller radius often settles it faster than dropping the feed.
Read position 2 first (negative vs positive), then the shape, then size and nose for the cut you are taking.
Every code below has its own page with the brand-neutral breakdown and equivalents across major makers, because the right insert might be a Sandvik number while your shop stocks Kennametal or Iscar.
Prefer the whole story on one page? These designations are decoded position by position — shape, clearance, tolerance, size, thickness, nose radius — with the practical trade-offs spelled out.
Free, no strings: 8-brand grade cross-reference (PDF) · ISO material-group cheat-sheet (PDF)