I'm looking to reknot my Rubberset 153 brush but I'm not entirely sure how to measure the knot size. I tried measuring it earlier today but I don't think I was doing it right. I was hoping you more experienced gents could help me out.
Tex, if I understand rightly you are just looking for the mechanism of measuring the knot size, right?
I haven't searched the first referenced thread, but here's some simple suggestions.
If you have an outside caliper of any sort, that will do the trick. Sighting across a ruler can be misleading. You want to measure at the base of the knot of course, right where the hairs intersect the handle.
If you don't have calipers, you might have a carpenter's square or adjustable square? You could slide a piece of cardboard against the other side of the brush and, being careful not to press in and distort the hair, while keeping the cardboard at right angles to the ruler part, get a measurement that way. If in the U.S., you'll have to multiply inches (converted to decimal) by 25.4 to get millimeters.