I wanted a simple, compact, no frills folding key holder to keep in my pocket (I hate key rings and bulky items in my pockets). This solution is about the same size as my Swiss Army knife and it doesn't have any pointy bits to jab me in the leg.
Print flat, no supports. Enable ironing if desired.
Assemble using two machine screws, two nuts and four washers on either side of the keys (add more washers in between if stacking keys). The holes are 4mm wide and the recesses for the nuts are 9.5mm wide. The recesses for the screw heads are 7mm wide. I cut down two #6 screws using a Dremel for just the two keys.