How to Read a Carbide Insert Part Number: CNMG432 Explained
Choosing the correct carbide insert can be confusing when a product name contains a long combination of letters, numbers, chipbreaker codes, and grade designations.
However, an insert number such as CNMG432 is not random. Each character describes an important feature of the insert, including its shape, clearance angle, tolerance, size, thickness, and corner radius.
In this guide, we will break down the meaning of CNMG432 and explain how to use insert designations when selecting replacement turning inserts.
What Does CNMG432 Mean?
The ISO insert designation system is intended to communicate important insert features and dimensions through a standardized code.
Let’s look at each position more closely.
C: 80-Degree Diamond Shape
The first letter describes the insert shape.
In CNMG432, the letter C identifies an 80-degree diamond-shaped insert.
The 80-degree diamond shape provides a strong cutting edge and is widely used for general external turning, facing, and boring operations. Compared with sharper insert shapes, such as 55-degree D-style or 35-degree V-style inserts, the C shape generally offers greater edge strength.
A CNMG insert normally provides multiple usable cutting edges because it is a double-sided negative insert.
Common turning-insert shape codes
The correct shape must match the insert pocket and toolholder. A CNMG insert cannot normally be substituted directly for a DNMG or VNMG insert because the shape and holder geometry are different.
N: Zero-Degree Clearance Angle
The second letter identifies the insert’s clearance or relief angle.
The letter N means the insert has a 0-degree clearance angle. This is commonly called a negative insert.
A negative insert does not have built-in clearance below the cutting edge. Instead, the necessary clearance is created by the angle of the toolholder.
Because the insert is symmetrical, many CNMG inserts can be used on both sides. This gives the insert more available cutting edges and makes CNMG inserts a popular, economical option for general turning.
Negative inserts also tend to have stronger cutting edges than positive inserts. However, they usually generate greater cutting forces, so machine rigidity, workholding, and available spindle power should be considered.
M: Tolerance Class
The third letter describes the insert’s dimensional tolerance class.
The letter M is a commonly used tolerance class for general-purpose indexable turning inserts.
Tolerance class affects dimensional variation in features such as:
- Inscribed circle
- Insert thickness
- Corner location
- Overall insert dimensions
For many general turning operations, an M-class insert provides a practical balance between dimensional consistency, availability, and cost.
Applications requiring extremely precise edge location or specialized finishing may use a different tolerance class, but the insert must still match the intended holder and application.
G: Insert Type and Hole Configuration
The fourth letter describes construction features such as the center hole, countersink, and chip-forming geometry.
In a standard CNMG designation, the letter G identifies a hole and chipbreaker-style configuration commonly used with mechanical clamping systems.
The exact chipbreaker geometry is not fully identified by the letter G. Manufacturers normally add their own chipbreaker code after the basic designation.
Examples include:
- CNMG432-EGU
- CNMG432-ENG
- CNMG432-EMU
- CNMG432-CQ
- CNMG432-MP
- CNMG432-MM
These suffixes are manufacturer-specific. Two inserts may both be CNMG432 but perform very differently because their chipbreakers are designed for different depths of cut, feed ranges, materials, or cutting conditions.
4: Insert Size
The first number in 432 represents the insert size.
For the ANSI designation CNMG432, the number 4 indicates a nominal 1/2-inch inscribed circle.
The inscribed circle is an imaginary circle that fits inside the insert and touches its sides. It is commonly used to describe the overall insert size.
The equivalent metric designation is generally:
CNMG120408
In the metric code, 12 corresponds to an approximately 12.7 mm inscribed circle. Seco lists CNMG120408 and CNMG432 as equivalent metric and ANSI designations, with a 12.7 mm inscribed circle.
3: Insert Thickness
The second number indicates the insert thickness.
In CNMG432, the number 3 represents a nominal thickness of:
3/16 inch, or approximately 0.187 inch
The corresponding metric CNMG120408 insert has a listed thickness of approximately 4.76 mm.
Insert thickness matters because the insert must sit correctly in the holder pocket. A similar-looking insert with a different thickness may not fit securely or may place the cutting edge at the wrong height.
2: Corner Radius
The final number identifies the insert’s corner, or nose, radius.
For ANSI turning-insert designations, the number is generally expressed in sixty-fourths of an inch.
Therefore:
2 = 2/64 inch = 1/32 inch = 0.03125 inch
The metric equivalent is approximately:
0.8 mm
Common corner-radius codes
| ANSI code | Approximate radius |
|---|---|
| 1 | 1/64 in. or 0.4 mm |
| 2 | 1/32 in. or 0.8 mm |
| 3 | 3/64 in. or 1.2 mm |
| 4 | 1/16 in. or 1.6 mm |
A larger corner radius usually provides a stronger cutting edge and can support heavier feeds. However, it may also increase radial cutting force and the risk of chatter on less rigid setups.
A smaller corner radius generally produces lower cutting forces and can be useful for lighter finishing cuts, but the edge is not as strong.
CNMG432 vs. CNMG431
CNMG431 and CNMG432 share the same basic shape, clearance angle, tolerance class, hole style, size, and thickness.
The primary difference is the corner radius:
| Designation | Corner radius |
|---|---|
| CNMG431 | Approximately 1/64 in. or 0.4 mm |
| CNMG432 | Approximately 1/32 in. or 0.8 mm |
CNMG431 may be preferred for lighter cuts, lower cutting pressure, or finer profiles.
CNMG432 offers a stronger cutting corner and is one of the most common choices for general medium turning.
The best option depends on the feed rate, depth of cut, part rigidity, tool overhang, and required surface finish.
The Chipbreaker and Grade Are Equally Important
Knowing that an insert is CNMG432 is only the beginning.
A complete product description may look like this:
Sumitomo CNMG432 EGU AC8025P
This designation contains three main sections:
- CNMG432: Insert shape and dimensions
- EGU: Manufacturer-specific chipbreaker
- AC8025P: Manufacturer-specific carbide grade
The chipbreaker helps determine the suitable feed range, depth of cut, chip control, and whether the insert is intended for finishing, medium cutting, or roughing.
The grade describes the cutting material, substrate, coating, wear resistance, toughness, and intended workpiece-material range.
For example, two CNMG432 inserts with different grades may be designed for completely different applications:
- Continuous steel turning
- Interrupted steel cutting
- Stainless-steel machining
- Cast-iron turning
- Heat-resistant alloy machining
For this reason, replacing an insert based only on “CNMG432” may not produce the expected tool life or chip control.
Will Every CNMG432 Fit the Same Holder?
In many cases, inserts sharing the same standardized CNMG432 geometry will physically fit a compatible CNMG 12 or CNMG 4-size toolholder.
However, always confirm:
- Toolholder insert designation
- Seat size
- Clamping system
- Shim configuration
- Insert thickness
- Corner-radius clearance
- Manufacturer recommendations
Even when an insert fits physically, the chipbreaker and grade still need to match the workpiece material and cutting conditions.
How to Select the Right CNMG432 Insert
Before choosing a CNMG432 insert, identify the following information:
1. Workpiece material
Determine whether you are machining carbon steel, alloy steel, stainless steel, cast iron, aluminum, hardened steel, or a heat-resistant alloy.
2. Type of operation
Decide whether the operation is finishing, medium turning, roughing, facing, profiling, or interrupted cutting.
3. Cutting conditions
Consider:
- Cutting speed
- Feed per revolution
- Depth of cut
- Coolant availability
- Continuous or interrupted cut
- Machine and workpiece rigidity
4. Required chip control
The chipbreaker should match the expected feed and depth-of-cut range. A finishing chipbreaker used at a heavy depth of cut may overload the cutting edge. A roughing chipbreaker used at a very light feed may not break chips effectively.
5. Required grade
Select a carbide or cermet grade designed for the workpiece material and cutting conditions.
Final Summary
The designation CNMG432 tells you the insert’s fundamental shape and dimensions:
- C: 80-degree diamond shape
- N: Zero-degree clearance
- M: M tolerance class
- G: Hole and chipbreaker-style insert construction
- 4: 1/2-inch inscribed circle
- 3: 3/16-inch thickness
- 2: 1/32-inch corner radius
However, CNMG432 alone does not tell you the complete application. You must also evaluate the manufacturer’s chipbreaker and grade to determine whether the insert is suitable for your material and cutting conditions.
Download the Complete Technical Guide
Keep this CNMG432 reference guide for your shop, purchasing team, or machine operators.
Download the CNMG432 Technical Reference Guide (PDF)
