Insert Designations

Carbide inserts use a coding system of numbers and letters to describe their shape, dimensions, and important parameters. For example, the designation of the insert shown in Figures 11-16 is a CNMG-433.

Figure 17: Carbide Insert Designation

Shape (CNMG-433)

There are at least 18 different shapes of carbide inserts. The most commonly used are shown in Table 8.1 with their letter designation. The angle in this designation refers to the included nose angle at the cutting radius of the tool.

C80 degree diamond
D55 degree diamond
V35 degree diamond

Table 8.1: Common Insert Shape Codes

Clearance Angle (CNMG-433)

Clearance angle is the draft on the face(s) of the insert that contact material during machining. More about insert angles a little later.

DesignationClearance Angle
N0 Degrees (No Draft)
A3 Degrees
B5 Degrees
C7 Degrees
P11 Degrees

Table 8.2: Common Insert Clearance Angles

Tolerance (CNMG-433)

This is how much variation is allowed in the dimensional size of the insert. Tolerances described with this parameter include the corner point (nose radius), thickness, and I.C. Typical tolerances are shown in Table 8.3:


Table 8.3: Typical Insert Tolerances (Inch)

Hole/Chip Breaker (CNMG-433)

The hole/chip breaker designation describes both features with one letter. The hole in the insert and tool holder must match. If no letter exists in this field, then the insert does not have a hole to secure it to the holder, and is held by clamp force only.

DesignationHole ShapeChipbreaker Type
W40-60 deg, double c-sinkNone
T40-60 deg, double c-sinkSingle-sided
PCylindricalHi-double positive
ZCylindricalHi-double positive

Table 8.4: Common Insert Hole/Chip Breaker Configurations

I.C. Size (CNMG-433)

Inserts are measured by the diameter of an inscribed circle. I.C.'s range from .0625 in to 1.25 in. Table 8.5 lists the sizes you are most likely to use.

DesignationDecimal (inch)Fractional (inch)

Table 8.5: Common Inscribed Circle Sizes

Thickness (CNMG-433)

Insert thickness.

DesignationDecimal (inch)Fractional (inch)

Table 8.6: Common Insert Thickness

Nose Radius (CNMG-433)

Insert cutting nose radius.

DesignationDecimal (inch)Fractional (inch)

Table 8.7: Common Cutting Nose Radius

The insert shapes, sizes, and designations in these tables are just of few of what is available. Any lathe tool catalog or manufacturers web site will show many more.

It is not important to memorize every tool shape or designation scheme. It is important to know insert terms and specifications to understand insert recommendations from the tool representative or technical resource to select the correct insert for the application.