This might be helpful to those just getting into using carbide inserts.

[ltlvt]

Which part is unclear? There are several ways of specifying the size of an insert, the two common ones are cutting edge length (blech!) and inscribed circle (IC). I favor IC because it's easy to understand, and pretty easy to eyeball the difference if you stay away from the weirdo sizes. For instance, most of my inserts are either 3/8" or 1/2" IC - regardless of shape. IC is the biggest circle that can fit within the outline of the insert. So it's pretty easy to tell the difference between those two. In the examples given (CNMG432" / "CCMT32.51) the first has a "4" and would be a 1/2" IC, the second is a "3" and would have a 3/8" IC. Does that make sense?

The ISO code is the cutting edge length, so even for an insert with the same IC, the ISO designation can be different, depending on the shape. I consider it tedious and must refer to a chart like that above if forced to do so.
GsT

I understand IC I do not understand the 4 and the 3 nor do I understand the 32" or the 2.51"

 

[Aukai]

Introduction to indexible tooling by our own David P Best.

https://www.amazon.com/Introduction-Indexable-Tooling-Metal-Lathe/dp/B09K27XRQ5/ref=sr_1_fkmr0_1?crid=2NRM2VJSZ1FEI&dib=eyJ2IjoiMSJ9.480xi9gxfYSn-L1fvE64IAgD1ZoabftxUN3Xy9HaeiE.t-Q6cnzUHK-uDKP_jkX2lCqjfvimuodGUfEUe9mpo5U&dib_tag=se&keywords=introduction+to+indextical+tooling&qid=1724613460&sprefix=Introduction+to+indexible+tooling%2Caps%2C1003&sr=8-1-fkmr0

 

[GeneT45]

I understand IC I do not understand the 4 and the 3 nor do I understand the 32" or the 2.51"

The only numbers that matter here are the 4 and the 3. Those are the IC in 1/8" increments (4x1/8" = 1/2", 3x1/8"= 3/8"). The 32 and 2.51are not part of the size designation. Continue down the page I linked and you'd see that the next designations are Thickness - which is a 3, or 3/16" and 2.5 or 5/32". That leaves one digit on each, and that signifies the nose radius.

GsT