These are mounting brackets to attach 28mm (or smaller) hobby/RC brushless outrunner motors onto a board. Personally, I used them to make a 2x4 with an IMU that hangs from the ceiling and points in a given direction, based on serial commands for compass heading and pitch angle. You could make the same thing, or possibly just use these to test your motors and props. See a video of them in action here http://www.youtube.com/watch?v=UOM7koNqGE4