This is a simple print to build a set of darts for use on the International Space Station. In an interview with Chris Hadfield he said that one of the most prevalent issues on the ISS is actually boredom and gave the example of a darts game that he'd made out of a heavy object and some Velcro. This design is a refinement of that game for ease of use in a no gravity situation. The top is simply twisted off of the print and a 1/2 inch bearing ball is placed inside (or anything else that provides weight) the top is then reattached and the dart is ready for use. This design can also be used in swimming pools as a simple, fun looking, pool dart.