This is a knockoff lasercutter version of:
Windell H. Oskay from Evil Mad Science and Zach 'Hoeken' Smith helped work out the laser cutter design on the thingiverse mailing list.
This is just a first try. I cut one in 3/16" plywood and it's usable, but not ideal. It's clearly going to break soon. The biggest problem is the thinness of some of the walls. In the commercial version there's a recessed channel, rather than a cut out channel as in this design. That gives the tool more strength.
Cut it out on a laser! Cut numbers and index lines first, then channel and hanging hole, then outline. Colored coded for your convenience.