A group in a class I am TAing wanted to design a 3D printable foldable bottle opener. I decided to take my own crack at it. They had theirs fit into a 34 x 44 x 9 mm volume, so I had mine fit that as well.
Print it solid. use 3mm filament as hinge pins.
I printed mine on a Stratasys Uprint, which has a pretty good accuracy, so I used a very small clearance between the moving parts (.1mm). I included the solidworks file in case anyone wants to modify it, or if you don't have solidworks, let me know and I can post a version with whatever clearance you want.