Identify carbide parting insert?

Since my lathe is old and worn carbide tends to chip easily on it. Today I found a used parting holder and some Teledyne MP91M carbide inserts that I'd like to learn about. The damaged label appears to show MP91M and T?B?TN-21?4 and the inserts are inked MP91M, the holder has no markings and may not even be right for them, they seem to fit snugly without bottoming in the slot.
TIA