This is the cross brace for a quadcopter that I'm working on with a friend. The holes are made for 3/8" dia carbon fiber tubing that we got off of eBay. The design allows for set screws to hold the tubing in place and the center opening allows for the motor wires to be threaded through the tubing, and the octogon shape allows for the ESC's to be mounted around the outside. This was designed to be easily printed on a makerbot. I'm open to suggestions or ideas on improving the design. Current model is Ver4.Print. Install. Fly :) Goes with http://www.thingiverse.com/thing:13007