With my old no-name rotary tool I received a really nice desk clamp that I used a lot but when I have upgraded to Dremel 4000 it didn't fit into original clamp so I did model it in fusion 360 to make it wider.
Only hardware you need (apart from original no-name holder) is a m5x20 bolt with a nut (I stole mine from original holder too).
Base that fits the clamp has a diameter of 45mm, hole for Dremel has a nominal diameter of 52mm but can expand quite a bit if needed (only limits are bolt length and elasticity of the filament).
Unfortunately I can't find any online listings for similar holders, I got it many years ago from a local hardware store.
Printing tips: printed standing up without supports, you need to cut small pieces of plastic near the screw after printing.
The author marked this model as their own original creation.