@mmayo
I used the kits from Berea.
I have made several, but don't recall the drill size. I think I was successful just following the instruction sheet recommendation.
One point I want to make, though, is that I made all mine with a single long wood barrel.
It is easy to do that by first pressing the two brass tubes from the kit onto the center band and then turning off the excess centerband metal.
This results in one long brass tube. You then use a long blank and drill it . . If you drill carefully on the lathe you can drill from both ends
and the two holes meet in the middle with no problem.
The recipients of those pencils were happy with the single barrel modification