I had a couple similar on No2 MT with triangular inserts 9mm and 6mm across a side.
Presumably TPKN or TPUN (no idea what the difference is). I have searched the usual outlets but have not been able to find any replacement inserts at those small sizes. Had thought of trying a TCMT in their place, but I suspect they would break because of the hole, if used for milling.
Pity because they were very simple to use cutters and good for chewing out metal at maximum RPM on the mill. Finish was adequate for most jobs.