Head cover for a double-bit key. I made this model to print replacement for may old broken key head cover. First I tried to print it as one piece without supports, but at the hanging edge, the material sagged. 

Due to the fact that the metal key itself must be glued, I decided to make a case in two parts. It my opinion it was a success. Printed with PETG 0.2mm and 100% infill.

Size of my metal key head: length 15mm; width 15.65mm and height 2.3mm. Tube diameter 4.9mm.