Shave Handle and knot

Question?
If I buy a 24mm handle do I also buy a 24mm knot or a 23mm knot one size lower ?

You generally  want a knot with a diameter about 1mm smaller than the diameter of the handle socket at the top.

Thank you so much !

That's my understanding on knot diameter.  There is a lot of brush expertise on this forum, and perhaps others will post their views on your question.