Looks like we replied at the same time.
After reading the post above it seems they suggest a 1/16" cutter (1.6mm). Personally, speaking from experience you don't want to route a slot too small if the slot is close to an edge especially if you are using MDF as the force of installing the t-moulding into a tight slot can cause the wood to split.
I'm guessing a 1/16" cutter is the nearest imperial width cutter available 'over the pond'. If it was me, I would go with the 2mm.