Retailers who supply the knots are the ones that are suggesting what the hole size for the handle should be for a given size of knot. I do think that they would know what the norm is.
https://maggardrazors.com/collection...adger-fan-knot
From experience going by their recommended hole size for the handle still makes it a press fit not a sloppy drop in fit. The downside of having a too tight a fit is that over time the knot could swell enough with use to cause the handle to crack/split. I had that happen on a custom brush I had ordered.
Bob