ANSI vs ISO Insert Codes: CNMG432 Is the Same Insert as CNMG120408

The fax that started this guide had four words on it: CNMG432, 200 pcs. The European catalogue in front of me had no CNMG432 anywhere. It had CNMG120408, 680 cited ordering codes deep, and not one of them printed the number the buyer had written.

Both were right. CNMG432 and CNMG120408 are the same insert: same 80° rhombic body, same 12.7 mm inscribed circle, same 4.76 mm thickness, same 0.8 mm corner. One name comes from the ANSI-style inch convention used across North America; the other from ISO 1832. The letters are nearly identical, which is exactly why the mismatch causes so much trouble — people assume the numbers mean the same thing. They do not.

This guide is the conversion I use at the counter. Every mapping below is checked against the cited ordering codes in the InsertBase catalogue: 18,722 of 19,449 rows carry an ANSI code across 314 of 367 models. You can re-verify any row on the linked model page. For the complete list rather than the common examples, browse the ANSI insert code index — every code whose conversion reproduces its cited ISO model.

The letters agree; the numbers do not

Take the letter block first, because it is the part that survives conversion. CNMG means the same in both systems:

• C — 80° rhombic shape
• N — 0° clearance, negative insert
• M — medium tolerance class
• G — cylindrical fixing hole, chipbreaker on both faces

What changes is the size block. ISO 1832 writes it in metric tenths of a millimetre and standard size codes: 12 for the 12.7 mm circle, 04 for the 4.76 mm thickness, 08 for the 0.8 mm corner. The ANSI-style code compresses the same three dimensions into inch fractions: 432 — four eighths of an inch across, three sixteenths thick, two sixty-fourths at the corner.

There is one visible letter difference in positive inserts. ISO writes the thickness code with a letter in the middle — CCMT09T304 — while the ANSI-style code is all digits, CCMT3251. Same insert, same three dimensions.

What the three digits actually encode

Read the digits against the inch table, but read them one at a time, because the thickness digit does not use the same denominator as the other two:

The first digit counts eighths of an inch of inscribed circle, and the third counts sixty-fourths of an inch of corner radius. The middle digit is read against the thickness table for that insert family — a negative CNMG432 uses 3 for 3/16 in, while a positive CCMT3251 uses 2 for 5/32 in. Do not convert the middle digit mechanically; look it up.

The conversion table, built from cited rows

These are the fifteen most-catalogued designations on InsertBase, with the ANSI base block that appears most often in their cited ordering codes. The base block is the first seven or eight characters — the geometry — and it is stable across brands.

Notice the WNMG line. WNMG080408 and WNMG432 share a name, but the 08 block is not the same metric number as the 12 block on CNMG — the trigon geometry produces a 12.7 mm circle from size code 08, while the rhombic produces it from 12. This is exactly why converting by eye fails: the size code is not a universal metric value, it is a key into a shape-specific table. The decoder resolves both.

The suffix is where conversions go wrong

CNMG120408 is the clearest example in the catalogue. Of its 680 cited rows, 662 carry an ANSI code, and 476 begin with the base block CNMG432 — but those rows spell 222 distinct ANSI strings. The extra characters are chipbreaker and grade designations from each brand: CNMG432RP, CNMG432MP, CNMG432P, CNMG432MN, CNMG432FW.

The base block tells you the pocket. Everything after it tells you how the chip breaks and what the coating survives. Those suffixes are manufacturer-specific and must never be transferred across brands; the same two letters do not mean the same grade claim from two different manufacturers. That is the line the CNMG120408 selection guide walks through in detail.

Not every catalogue publishes an ANSI code

96.3% of cited rows carry an ANSI field, but the coverage is not total: 53 of 367 models have none. Those rows come from catalogues that publish ISO-only ordering codes — 133 ISCAR rows and 18 Korloy rows in the current set. A missing ANSI name is not a missing insert, and it is not a conversion failure; it is a naming choice by that manufacturer.

How I convert in practice

1. Match the letters first. Shape, clearance, tolerance and fixing must agree. CNMG to CNMG is safe; CNMG to WNMG never is, whatever the size digits say.
2. Resolve the ISO code to millimetres. Run it through the decoder, or open the model page. You want d1, s and rε in millimetres, not a guess from the digits.
3. Read the ANSI block one digit at a time against the table above — IC in eighths, thickness per the family table, corner in sixty-fourths.
4. Check the suffix separately. If the job depends on chip control or grade, compare the actual catalogue rows on the cross-reference finder, never the letters alone.

Two dimensional checks make the conversion self-verifying: all 12.7 mm inserts and all 9.525 mm inserts are grouped by thickness and corner, so a converted code that lands in the wrong group is visibly wrong before anything is ordered.

Quick answers

• Is CNMG432 the same as CNMG120408? Yes — identical ISO 1832 geometry. Only the naming system and the brand suffix differ.
• Is CNMG432 the same as CNMG120404? No. CNMG431 is CNMG120404; the corner is 0.4 mm, not 0.8 mm.
• Can I order CNMG120408 when the drawing says CNMG432? Yes, provided the suffix and grade are specified. The geometry is the same; the shelf label is not.
• Why do I see CNMG432LF? LF is a brand chipbreaker suffix on the same CNMG432 geometry, not a different insert size.

All counts in this guide were pulled from the cited rows on 3 November 2026 and are re-runnable on each linked model page. Where a manufacturer publishes no ANSI field, the guide says so rather than inventing a conversion. The rules for how catalogue data is gathered and corrected are in the editorial policy.