As much as there is supposed to be a "Standard" for this, every manufacturer has their own little variance to the scheme. Typically the final designation of the insert has to do with and edge prep that is not part of the standard. Or it might be they developed a new shape of insert that wasn't thought of at the time the ancient standard was scribed into the granite.
Shape, IC Size, Thickness, Side Clearance Angle, Ground or Molded Tolerance, Chipbreaker, Edge Prep or Special Features are what these Codes consist of.
It gets confusing when the IC Size is measured by 1/8" of inches, but they also throw in 5/32". Corner Radius is measured by 1/64" until you go sharper than 1/64" and they designate it by 08 or 04 standing for .008" or .004". Thickness is all over the place. Then don't forget, there is a METRIC Standard also. I like the metric sometimes. But it strays off also.
Typically for side clearance the higher the letter is in the alphabet the more clearance angle it is. A=3Deg, B=5Deg, C=7Deg, D=15Deg, E=20Deg and so on until you see N=ODeg because N stands for Neutral. So it gets confusing.
Then for the Tool Holder itself. There is some of the same concept taken from the insert but then the clamp style, approach angle, shank size and length comes into play. Then milling cutter bodies will designate coarse or fine pitch, arbor size, number of inserts, etc..
Then BE CAREFUL as many of the manufacturers do nice little things like make holders and inserts that have to be used together so as their competition can't come walking in with an insert that looks very similar but is now running .010 undercenter on a lathe, or doesn't quite fit into the milling cutter body like it should so it immediately fails and crashes your $400 facemill.
Ceratip makes a Swiss Style Turning holder that is capable of letting you index the insert without taking the holder out of the Gang Slide such as a Screw Type holder makes you do. But what they don't usually tell you that most of their competition's inserts don't have the same counterbore dimensions so their locking pin doesn't secure that insert in place and fails quickly usually causing a wreck. So as soon as you put the Ceratip insert back into this holder you have success AGAIN. Keeps you using their insert. Don't get me wrong, Most Every Tool Manufacturer has doen this type of trick. Carboloy used to make inserts that were thicker than most everyone else Standard insert. When used with their holder the centerline height was correct. Put in someone else's insert and it wouldn't have a chance.
As a Tool Salesman you soon find yourself doing some honework, bringing the holder and insert combo in to test. It's a little more work, but success outweighs failure every time.
Every Insert Section of Tooling Catalogs try to show all of this stuff. Mitsubishi has one of the best I refer to for the basics of it all.
Then there's threading, drilling, etc etc...... Good Luck
JR