second number represents the thickness of the insert.
This is measured in 1/16” increments in the ANSI system (3
x 1/16” = 3/16” = 0.1875”).
In the ISO system the thickness is measured in increments of
The Insert Nose Radius
most critical dimension on an insert is the nose radius.
CNC programs are written around a specific insert nose radius
size because the nose radius leaves its shape (form) on the part.
If you change TNR size of your insert you must also change
the CNC program.
In the ANSI system, the third number represents the TNR.
The nose radius of an ANSI insert is based on 1/64”
TNMG-432 insert would have a 0.031” nose radius.
The third number is 2 (2 x 1/64” = 1/32”).
The ISO system is a conversion from the ANSI system, in metric
values. This conversion can be done by using the conversion factor
of 1” = 25.4 mm.
convert the metric number to the inch equivalent is easy. For
a CNMG-19 06 16 insert,
25.4 = 0.063”
When using ISO (metric) inserts we must verify that the nose radius
on the insert matches the nose radius used in the part program.
If in doubt convert the number to find the equivalent inch
addition to these informative and descriptive numbers, many insert
manufacturers are now placing speed and feed recommendations on the
This is very helpful and gives a good range for standard
Another helpful piece of information I’ve always wanted to see on
the insert box is the TNR size.
We know that the TNR value can be calculated as we’ve done
above, but when you’re sorting through a cabinet full of blue, red
or yellow boxes it would be very helpful to see the TNR with a quick
This is the most important piece of information in terms of
machining so it makes sense to make it handy for users.
the next time you see an ISO insert, it is not that different from
an ANSI and may even be easier to understand.