Customizable ER Collet Box
This is a customizable collet box for all ER types. I have only printed the one for ER20 (STL File attached), but it is based on mathematical calculations of all ER sizes, so basically I do not see any reason not to work for the rest.
ER32 and ER40 are kind of large for printing, but I just have them to complete the whole ER set.