A small (2.0cm) cube designed for mass production and giveaways! It also serves as a pretty good calibration print for all sorts of printers, and one cube only takes 30 minutes to print with a raft and supports. I've also included the original Inventor file in case you want to change the tolerances (the gap between the cube and sphere is 1mm currently).

Print with supports! A raft is recommended, since it prevents the center from dislodging.