The object that is inserted can vary in size a little. I was thinking if the shell had a number of fingers extending inside at a angle they might be able to both hold the object in place and also allow them to work with some objects that vary in size a little bit. The fingers would flex like a spring. Also wondering which type of filament would be best for this, but first have to figure out how to draw the shape.

I have drawn a hollow shell and have some slots cut in it on two sides. That is where I'd like the fingers to be, when the object is inserted they would move into the area where the slots are. Here is a link to that:

https://cad.onshape.com/documents/75ce9d024accbadf93f11982/w/15c1e72dea1641eb3172fe44/e/f6402a33f55e6168f21c75a1?renderMode=0&uiState=6a1a68bc7db5c27cae5c5a63

I don't know if this is an approch that would work. I did try to just do some flat sketches and try to extrude a little, then draw the angled parts and extrude some more and repeat, but got nowhere.

I see there are some sheet metal tools, I wonder if something like that might be able to create the fingers, tabs or whatever this sort of thing would be called.