Summary

A simple mount for a round on-off switch such as http://www.amazon.com/dp/B00BQEK26Q/ref=pe_385040_127745480_TE_item. It attaches to a 2020 extrusion with two M5 bolts.

There is a strange artifact between the two bolt holes, which I have not been able to eliminate. It may be a problem with Blender's STL export code.