Customizable OpenBeam/misumi/slotted extrusion double T bracket

A standard T-bracket (eg http://www.thingiverse.com/thing:30524) doesn't work when you need to place two parallel extrusions closer than 3x the extrusion width apart (45mm for OpenBeam/misumi). To work around this I've created the double T bracket. You may adjust the T-spacing as you wish to achieve any spacing from flush to arbitrarily far. This may also help when precise spacing is required.