This was designed for a Proxxon MICROMOT 60/E (tool similar to a Dremel) rotary tool.
I used it with a tiny drill to make holes in the sides of small cylinders.
Fusion 360 file attached so you can customise it for your tool!
Apologise for the messy Fusion 360 file, this has been sitting on my computer ready to upload for a few years, I just never got around to it.
20mm diameter collar for the rotary tool
5mm diameter hole for the fastener to tighten the collar
The author marked this model as their own original creation.