I've had this prepared handle and knot kicking around for ages as an unfinished job when I sorta let shaving take a back burner for a year or so.
Details are entirely forgotten, but I do know it's a BrushWorks Scanlon which must have come with a badger knot or some uninspiring synthetic for me to have drilled it out. I do recall boring the handle out a little as I wanted a bigger knot and can find receipt evidence or buyng a Cashmere knot at 24mm, so I think that's the specifics.
Here's the finished article ...
A-ha! I've found an older photograph. Looks like the knot simply came out with mole grips and a twist. Seemingly, I thought the knot too rubbish to even try to save. You can see the hole is bored out a little and smoothed, ready for the next knot.
I used this brush last night, whipping up a light lather of T&H No 18. Super-soft and absolutely perfect for cream lathering ... even on the face. I don't foresee any issues with it loading up a hard soap. That's tonight's shave with MWF.