Since this is a "press fit", simply scale one percent larger or smaller, it should not fit right away or help with a hammer, when... hitting the cap do not hit the hook.
To connect the hook and the cap, simply use an M2x10 screw or a two-component glue, that's fine.
The files are made for pipes with an outside diameter of 20mm and a wall thickness of 1mm or 2mm.
I use these caps for my wall coil holders, for example.
I would be very happy about a small https://paypal.me/d23elt05a donation or a picture of your print, and would be happy if you visit my other Designs. :)