This is a bracket to hold a keyed 5/8 inch shaft with a 5mm key; these are made to go along with the window motor and adapter shipped in the FIRST Robotics Kit of Parts.
They also work in conjunction with: http://www.thingiverse.com/thing:234751
Printed on a Cubify 2 with rafting and solid on.
These are strong; but are still plastic; so the keyway may strip-out if enough force is put on them. Test thoroughly before competition!