Replacing my first knot on a vintage brush. I know its been asked a million times, but in searching I am getting conflicting stories. The hole in this handle measures 20mm across. So to me that means I need a 20mm knot an set the loft to where I prefer. I have read that some people use a size smaller for fitting? So I am ready to purchase a knot but don't want to order the wrong size. Thanks for any help.