Some of you more enterprising / handy folks out there in Brewland want to put your FTSs coil(s) on the side (inside) of your fermenter body instead of the FTSs flat lid (so that you can maintain the domed lid for transfers, etc..)
And yes, finding a metric step bit that just happens to have one of the steps at 17mm on the nuts is indeed tricky. For ref / FYI, our units are all punch with a17mm punch (not drilled) - so that's how we get them perfect 17mm.
And there is good reason for that size - but we won't bore you with all the design backgrounder there - is what it is, so now you are asking how do i get there?!
So yeah - start with a 5/8" and if too small then go to an 11/16th.
Kind of like a haircut - if it's too long you can still cut some off. Too short, and well your hair is now too short! So start with 5/8" on your bit / Chronical and see if your fitting will fit up. If not, then go into the 11/16th. 17 mm is a "tweener" there.
And also we are looking now for a supplier to just make us a custom 17 mm bit and sell on our site.... Stay tuned there!