Knot Room?

I got 3 beat up brushes today. 1 was totally shot, the second would never survive restoration but the third came apart quite nicely. I had a 22mm boar knot from one of the other brushes that seemed to be the correct size but just wouldn't go in the hole even after a little sanding to even out the crooked plastic collar.

So I assume a 20mm would fit in rather easy. When installing a new knot should there be a tiny bit of room for the epoxy or should the knot fit pretty snug? That 22mm was hard to fit in there even half way with some pressure but after that just wouldn't go even though there seemed to be enough room.:shrug:

I have an old Hickory ax handle end I'm going to round off to replace the cheap black copper thingy that's currently on the handle.