This is a mild remake of Loclhst's excellent Z-Axis endstop. I used an M3 16mm Bolt, and Nut I had to modify it slightly, because although it worked for his OneUp perfectly, it didn't work well for my TwoUp. All I did was move the stuff around, and cut a nut holder. So honestly, all the credit goes to Loclhst.This was a simple remake of Loclhst's excellent Z Axis Endstop. When mounting it, just make sure you reverse the switch compared to his other end-stop. You want the switch button as close to the axis rod as possible. As you should be able to see in my picture.