About this 3D model

For a nice linear slide modification, I need to be able to attach a smooth rod in a T formation with a threaded rod. This thing will allow you to thread 5/16" rod in one direction, and slip 5/16 rod into the other axis (the diameter is enlarged for sliding vs threading). The thing is in the shape of a cube, and has the same dimensions as this thing: http://www.thingiverse.com/thing:5645