This is a bracket designed to hold a 12MM diameter inductive sensor to the print carriage. It simply sandwiches between the carriage and extruder, so it should work with pretty much any extruder setup. The holes are 23mm center-to-center, so it may also fit prusa models.
Update 2016-01-05: Beefed up bracket, as the original one could bend as the wire bundle pushed on it. Also added a nut trap for the top nut, making adjustment easier.
Here is a video of it in action, used for auto bed leveling: https://www.youtube.com/watch?v=xtBFl8jm9xA