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I'm not the greatest brush maker, but I'll try and kill a boar this week and take pictures of making a brush next weekend.

:)
I'm sure someone sells a hair stacker just for brushes - it's probably a pvc coupler that costs $50.
I purposefully chose the fishing line for it's strength to diameter ratio, it's waterproof,...

I've made a few boar knots and they weren't that hard to make. I didn't get enough hair into the first couple, but by the 5th attempt I had it down.
I used a 1" pvc pipe coupler as a hair stacker....