How to Read a Carbide Insert Identification Chart

Why the ISO 1832 code exists

An indexable insert is identified by a standardized code — ISO 1832 / ANSI B212.4 — that every manufacturer in the world uses. Read it correctly and you know the insert\u2019s shape, size, thickness, nose radius, cutting edge style, and often its chip breaker and tolerance class, without opening a catalog.

This matters twice: when you order (one wrong digit and the insert does not fit your holder) and when you stock (a machine shop with a dozen insert codes needs to know exactly what each one is). The code is printed on the insert box and often lasered on the insert itself.

The code, position by position

Take a typical code: CNMG120408. It has 4 letters, 4 numbers and an optional suffix. Here is what each position means.

Position 1 — shape (letter). The insert\u2019s basic shape: C = 80° rhombic, D = 55° rhombic, V = 35° diamond, T = triangle, S = square, W = trigon (80° three-cornered), R = round, L = rectangular. The shape defines what angles the tool can present to the workpiece.

Position 2 — clearance angle (letter). The relief angle on the insert side: N = 0° (negative), A = 3°, B = 5°, C = 7°, P = 11°. Negative inserts (N) are the strongest and use both sides — eight edges on a CNMG. Positive inserts (C, P) cut with lower force but have fewer edges.

Position 3 — tolerance class (letter). Dimensional accuracy: A, F, C, H, E, G, J, K, L, M, U. H and G are precision classes for finishing; M and U are general classes. Most standard inserts are M or U class, which is fine for general machining.

Position 4 — type (letter). Whether the insert has a hole, chip breaker or clamping features: N = no hole, R = hole without chip breaker, M = hole with chip breaker on one side, G = hole with chip breaker on both sides, T = hole with chip breaker on both sides and countersink. Most modern turning inserts are M or G type.

Positions 5-6 — inscribed circle (number). The insert\u2019s size in millimetres, measured as the inscribed circle: 06 = 6.35 mm, 09 = 9.525 mm, 12 = 12.7 mm, 16 = 15.875 mm, 19 = 19.05 mm. In the example CNMG120408, 12 means 12.7 mm.

Position 7 — thickness (number). Insert thickness in 1/10 mm, with decimals dropped in some cases: 04 = 4.76 mm, 08 = 6.35 mm. CNMG120408 has thickness 4.76 mm.

Position 8 — nose radius (number). The corner radius in 1/10 mm: 02 = 0.2 mm, 04 = 0.4 mm, 08 = 0.8 mm, 12 = 1.2 mm. CNMG120408 has a 0.8 mm nose radius — the most common general-purpose value.

Suffix — chip breaker and grade. After the main code, a suffix identifies the chip breaker design and often the grade: for example CNMG120408-MP or CNMG120408-GH. The chip breaker affects chip control at different feeds and depths of cut; the grade affects hardness vs. toughness.

Common shapes you will meet

In a typical turning workshop you will stock a small set of shapes:

CNMG — 80° rhombic, negative, 8 edges. The general-purpose workhorse for steel and cast iron turning. Strong nose angle, good for most operations.

DNMG — 55° rhombic, negative, 8 edges. More clearance for profiling and copying where the tool must reach into corners.

VNMG — 35° diamond, negative. Maximum access for narrow profiling and finishing in tight spots, at the cost of nose strength.

WNMG — 80° trigon, negative. A compromise: strong like a square insert but with a sharper effective cutting edge — a very popular general-purpose line.

CCMT — 80° rhombic, positive, 4 edges. Low cutting forces, ideal for thin-walled parts, aluminum and finishing on machines with limited rigidity.

Grades: the last two positions

The ISO application group is the short hand every buyer should know: P = steel, M = stainless steel, K = cast iron, N = non-ferrous (aluminum), S = heat-resistant alloys and titanium, H = hardened steel.

A grade like P20-P35 means the insert is designed for steel turning in the middle of the P range — general machining. Grades get their properties from the carbide substrate (tough or hard) and the coating (CVD multi-layer for wear at high speed, PVD for sharp edges and stainless, uncoated for aluminum where sharpness matters most).

Rule of thumb: roughing needs a tougher grade (lower number ranges), finishing needs a harder, more wear-resistant grade. If one grade must do both, choose the middle of the range and adjust speeds and feeds accordingly.

Buying inserts with the code

When you order, the complete code — for example CNMG120408 with an MP chip breaker and a P25 grade — tells your supplier exactly what to send. If you are sourcing from a factory like ours, include:

The full ISO code (shape, clearance, size, thickness, nose radius)
The application group (P/M/K/N/S/H) and your workpiece material
The operation: roughing, semi-finishing or finishing
Your machine\u2019s rigidity and spindle speed range
Quantity and packaging preferences

Get those five things right and the inserts you receive will match the chart every time. If you are unsure which code fits your holder, send us the code printed on the box of your current insert — we will match it or suggest a better grade for your application.