This is a very simple hinged clamp with catch. It is designed to attach something to a strap (or other flat thing) up to 54mm wide. As an example, I have used it to mount something on my guitar strap.

Build your thing with this on it, or simply use glue to attach it after printing.

Print the inner and outer pieces separately. You will need to print with a very small amount of support on both for the hinges. Remove the support and file the hinge surfaces flat so that they mate cleanly. Drill out the hole in the center of the hinge with a small drill bit (I think a 5/64 should work), and insert a short piece of 1.75 mm filament. Heat and mushroom the ends of the filament so it can't fall out.