The gal didn't mention the hook size in the video. My daughter and I think it's about a K 6.5 mm hook. I tried this last night on worsted weight yarn and it's about right. If you're using bulky weight, you may go up to maybe an 8 mm. I believe that's a size N in Boye hooks. The sizing for my Bates hooks run a little differently that large. Their N is a 9 mm,don't know why. So the Bates 8 mm is an L or M hook. I'm visiting at my daughter's so of course left the majority of my set at home can't check for sure.