how does one determin the right size carbide insert

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I bought some carbide inserts for my lathe turning tool, only to find out i got the wrong size.... I bought insert #321 TNMP Triangle shape, My book says that the 321 has a IC of 3/8. so where does the 3/8 come into play, what does I C stand for... I thought the 3/8 mint  each side of the triangle was 3/8" which is what i need, but I'm wrong cuz these have a side length of 5/8" WAY to big....so how do i measure?
Reply:Insert size is determined by what size circle will fit into the shape of the insert.  That is why your "3/8" insert measures 5/8 corner to corner.
Reply:IC = Inscribed circle Your tool holder is cut for a specific size and shape of insert along with a matching seat (if required)THis is a link to a PDF that goes into a lot of detail on what exactly each dimension of an insert is and how it is referenced as well as geometries etc.  It gets a little technical but there are several printable pages that are handy to keep close when you start shopping for carbides.http://www.ccpa.org/pdf/B212_4.pdfAnother good reference would be http://books.google.com/books?id=88n...0guide&f=falseIf you could give the exact dimensions of the pocket in your holder I could tell you the general size, altough the exact insert itself would vary according to your application.
Reply:OK... now i think i can figure out the right one.....I didn't know that, ya learn something new every day.................