A turning insert code such as CNMG 120408 is read one position at a time. The first four letters give the shape, clearance angle, tolerance class and hole or chipbreaker type. The three pairs of digits give the size, the thickness and the corner radius. The code follows the ISO 1832 system, and the insert shape is the same letter group that names the holder it fits.
CNMG 120408, position by position
Position
Characters
Meaning
1 Shape
C
80 degree rhombic (diamond)
2 Clearance angle
N
0 degree clearance
3 Tolerance class
M
Medium (moulded) tolerance
4 Type
G
Hole in the centre, with a chipbreaker
5 Size
12
Size code; on this insert it goes with a 12.7 mm (1/2 inch) inscribed circle
6 Thickness
04
4.76 mm (3/16 inch)
7 Corner radius
08
0.8 mm
Anything written after these characters, such as a chipbreaker name or a grade, is added by the insert maker and is not part of the ISO code.
1. Shape letter
Letter
Shape
C
80 degree rhombic
D
55 degree rhombic
T
60 degree triangle
V
35 degree rhombic
W
80 degree trigon
S
Square, 90 degree corners
R
Round
2. Clearance angle
The second letter is the clearance angle under the cutting edge.
Letter
Clearance
N
0 degree
A
3 degree
B
5 degree
C
7 degree
P
11 degree
D
15 degree
E
20 degree
F
25 degree
3 and 4. Tolerance class and type
M is the common moulded tolerance. G is a tighter, ground class. In the fourth position, G as in CNMG means an insert with a central hole and chipbreaker features, made for use on both faces.
5 to 7. Size, thickness and corner radius
Thickness: 02 is 2.38 mm, 03 is 3.18 mm, 04 is 4.76 mm, 06 is 6.35 mm.
Corner radius, in tenths of a millimetre: 04 is 0.4 mm, 08 is 0.8 mm, 12 is 1.2 mm.
The size digits are not the same measurement on every shape, so read the maker's table for the shape you are buying.
How the insert code ties to the holder
The first letter group of the insert is the one the holder is made for. A holder for CNMG inserts does not take TNMG inserts. These are the turning holders listed by their own product pages:
Note the TNMG holder range: the four inserts it lists, 160402, 160404, 160408 and 160412, differ only in the last pair of digits, which is the corner radius (0.2, 0.4, 0.8 and 1.2 mm by the radius codes above). To read the letters on the holder itself, see how to read turning holder codes.
What to check before you order
Match the shape and size letters and digits to the holder's product page.
Choose the corner radius for the job; a larger radius is stronger, a smaller one suits finishing.
Check the hand and shank size of the holder (20x20 or 25x25).
