Any CAD users?!

[Redherring]

Hi

It's a big ask I know but...

I'm looking to have a 1 off shape 3D printed as a little project. It's basically a large egg shape. I found a CAD file for it, however rather than having it as 1 peice I was hoping to have it as 2 where the top part screws into the bottom part... assume that's possible for 3D printing.

The local library has a 3D printer and just needs the file. Don't suppose anyone could modify the file I have to make it into a screwn on top please?! I've never used CAD software before 

Thanks