They make this insert with many different configurations of chip breaker, positive/negative cutting geometry, and so on. The more common insert is the APKT style as Bruce mentioned above. The one you show in your picture I'm sure was designed to cut a certain material like cast iron, which will have a more neutral corner to the insert than the APKT has. And no, I have no clue the letter configuration for you insert. I bet the APKT style insert will fit the face mill you have there just fine.