It's a carbide single flute 2mm cutter, can't use a 3mm as the slots are 3mm (would leave too much trimming of the slots to make them square) and some holes are 2mm. I've tried 2 flute cutters but they lift the balsa and ply too much. Also if I go much faster the splined joints don't fit as well. I'm still learning so no doubt feeds will increase once I get used to it!