Customer of mine currently uses PCD tipped TPG 221 inserts to bore holes in 8%Si cast aluminum on his VMC. I came across a large lot of surplus Kennametal diamond coated TPG 221 inserts that are at a steal price. Im curious of how the KD100 PCD tip grade compared to a KCD25 spray diamond grade?? Anyone have any experience? From what I can tell, the KCD25 is good for cast and abbrassive materials just like the KD100. Just lookin for some more info. Also, how does the Teledyne TDC21 grade compare to the KCD25?