This is a very good 6mm router bit. It makes vertical cuts in one direction, and when withdrawn, the lower cut clears the groove. Very fancy BUT the stem is NOT 1/4 inch. It's .23622, not .2500. Therefore, it is very weakened in the milling chuck. On first use it went from .250 to .325 before I noticed. I've calibrated and tightened it beyond what I normally do and everything works fine after that. So when you buy this cutter, remember that it needs to be a very snug fit and check between cuts.