A turning insert designation like CNMG 120408 is not random. Each position of the ISO 1832 code 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 nomenclature 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.
Most turning insert designations stop after seven positions. When a code carries more — CNMG120408-TF, DCMT070204R, CCMT060204-WP — the trailing characters are where the standard hands over to the manufacturer, and that is exactly where most misreads happen. ISO 1832-1 defines positions 8 and 9. Everything after them is either a different standardised field or a vendor's own code, and the two are worth telling apart before you assume two inserts are interchangeable.
| Pos | Field | Codes and meaning | Standard |
|---|---|---|---|
| 8 | Cutting edge form | F sharp · E honed · T T-land (chamfered) · S honed T-land (chamfered + rounded) · K double-chamfered · P double-chamfered and rounded. Edge prep decides how much abuse the edge takes before it chips: sharp cuts cleanest and breaks soonest, honed and T-landed survive interrupted cuts. It also governs plastic lowering: a chamfer reinforcing the rake near the edge markedly reduces the creep-driven collapse of the wedge in hot, difficult-to-machine work, with an optimum chamfer width well below the uncut chip thickness. | ISO 1832-1 |
| 9 | Insert hand | R right · L left · N neutral. Only meaningful on shapes that are not symmetrical about the cutting corner; a neutral insert works in either hand of holder. | ISO 1832-1 |
| 10 | Manufacturer extension | Vendor-specific suffix, usually after a dash: chipbreaker plus grade, e.g. a -PM or -RP style code. Not standardised — identical suffixes from two makers do not mean the same geometry. | Vendor extension |
| 11 | Edge prep class | L light (sharp or lightly honed / T-landed) · G general (medium hone / T-land) · H heavy (large hone / T-land). Appears in hard-turning part numbers after the cutting edge form. | Kennametal extension |
| 12 | Rake face angle | N 0° or less · A 3° · B 5° · C 7° · P 11° · D 15° · E 20° · F 25° · G 30°. The same letter-to-angle convention as position 2, applied to the rake face rather than the flank. | ISO 1832-1 |
| 13 | Added info | J polished rake face · P partial T-land · W wiper / radiused facet. A wiper is the one to notice: it changes the finish you get at a given feed. | Vendor extension |
Positions 1 to 9 and 12 are standard fields: two inserts that agree there agree on geometry. Positions 10, 11 and 13 are not a common language — they are the maker's own shorthand for chipbreaker, edge prep and grade. So CNMG120408 from two brands is the same shape, size and radius, while the part after it is precisely the bit that is not comparable. That is the whole reason a cross-reference has to be built from verified catalogue data rather than by matching suffixes.
One honest limit on the number block: position 5 is a size class, not a millimetre dimension. The exact cutting edge length and inscribed circle depend on the shape, so a 12 on a square is not the same edge length as a 12 on an 80° rhombic. Thickness and nose radius are direct (04 = 4.76 mm, 08 = 0.8 mm); edge length is not, and we will not guess it for you — read it off the maker's drawing.
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) · US ANSI/ISO reference pack ($9, printable) · Speeds & feeds wall chart ($5) · Shop-floor field guide ($12, 16 pages)