Plastic rivet for the cars engine splash shield, etc. Made this 6.5 mm in diameter and 12 mm long for a Toyota Avensis. Same type of design as: http://www.thingiverse.com/thing:264957 but needed a larger head. Use a 10mm M3 or similar (hole diam. 3mm).
An original rivet (broken) is seen to the right in one of the pictures.

Use 100% infill and preferably a slower extruder velocity, 50 mm/s.