I have a very low Z on my Prusa I3 so I designed this Hall-O holder to fit in the limited space since I couldnt find one already made. I glued the magnet to an existing adjusting screw I had on my machine, but it can be mounted as you want. The clamp works with the very limited space between the smooth rod and motor coupler on my machine. It's working great and I get a much more consistent z height over using a micro switch.I used ABS, but imagine any plastic will do. Printed on a MendelMax 1.5.