CNMG 120408 Carbide Turning Insert: The Complete Buyer’s Guide

If you run a CNC lathe shop or manage tooling procurement, chances are you’ve come across the code CNMG 120408 more than once. It’s one of the most widely used indexable carbide inserts in the turning industry — and for good reason. In this guide, we’ll break down exactly what this insert is, what its code means, where it performs best, and why it deserves a permanent spot in your tool crib.

What Is a CNMG 120408 Insert?

The CNMG 120408 is an 80° rhombic (diamond-shaped), negative rake, double-sided indexable carbide insert used primarily for external turning operations on CNC and manual lathes. Its negative geometry gives it exceptional edge strength, making it a go-to choice for roughing, semi-finishing, and general-purpose turning where durability and reliability matter as much as finish quality.

Because it’s double-sided, each insert gives you four usable cutting edges, which means less downtime for tool changes and a lower effective cost per edge — a detail that adds up fast across high-volume production runs.

Decoding the Code: What Does “CNMG 120408” Mean?

Every character in the ISO designation tells you something specific about the insert’s geometry. Here’s the breakdown:

Code	Meaning	CNMG 120408 Value
C	Insert shape	80° rhombic (diamond)
N	Clearance angle	0° (negative insert)
M	Tolerance class	Medium precision
G	Hole and chip-breaker type	Cylindrical hole, chip breaker on both faces
12	Inscribed circle (IC) size	12.7 mm
04	Thickness	4.76 mm
08	Corner radius	0.8 mm

Once you know how to read this code, you can quickly identify or compare any ISO-standard insert on the market — a genuinely useful skill for anyone specifying tooling.

Key Specifications at a Glance

• Inscribed circle (IC): 12.7 mm (± 0.08 mm)
• Cutting edge length: ~12.9 mm
• Thickness: 4.76 mm (± 0.13 mm)
• Corner radius: 0.8 mm
• Cutting edges: 4 (double-sided)
• ANSI equivalent: CNMG 432

These dimensions make the CNMG 120408 a mid-size insert — strong enough for moderate-to-heavy cuts, yet compact enough for good chip flow and finish control on general-purpose jobs.

Where the CNMG 120408 Excels

This insert is a workhorse across a wide range of turning applications:

Facing operations — the 80° cutting edge gives strong support at the tip, which holds up well under interrupted or facing cuts.

Roughing and semi-finishing — the negative rake geometry and thicker cross-section make it ideal for removing material quickly without chipping the edge.

Profiling and general external turning — its versatile shape lets it handle a variety of workpiece contours without frequent tool changes.

Materials machined: carbon and alloy steels, stainless steel, cast iron, and — depending on the grade and coating selected — brass, bronze, aluminum, and select high-temperature alloys.

Typical feed rates (on medium-stability alloy steel setups) run roughly:

• Finishing: 0.21–0.29 mm/rev
• Medium cuts: 0.42–0.57 mm/rev
• Roughing: 0.51–0.69 mm/rev

Actual parameters will vary depending on the insert grade, coating, machine rigidity, and material hardness — always check the manufacturer’s cutting data sheet before setting feeds and speeds.

Why Buy CNMG 120408 Inserts From Us

• Four cutting edges per insert — double-sided design means better value per piece and fewer changeovers.
• Consistent quality and tight tolerances — every batch is manufactured to ISO 1832 standards for reliable, repeatable performance.
• Wide grade and coating selection — whether you’re cutting soft steel or tough stainless, we stock grades matched to your material and application.
• Bulk and single-piece availability — order what you need, from trial packs to production-volume lots.
• Fast, reliable delivery — so your line doesn’t stop for tooling.

If precision, durability, and cost-per-edge matter to your shop floor, the CNMG 120408 is one of the smartest additions you can make to your turning tool inventory.

Ready to Order?

Get in touch with us today for pricing, bulk discounts, and grade recommendations tailored to your application. Whether you’re machining mild steel or hardened alloys, we’ll help you find the right CNMG 120408 insert for the job.