On the i3 with a newer generation J-head hotend (very short) there's almost no room for the endstop at the bottom of travel so I had to make this hold the thing off to the side enough for the PCB to clear the motor mount.No fine adjustment is needed since there's an adjustment on the electronics.The mounting lugs are offset to place them directly under the motor mount on the Prusa i3. You could fiddle with the SCAD to do any offset you want. The SCAD code is pretty clean so the parameters should work well.Instructions:The STL will probably be fine if you're using M3 hardwareThe shorter screw just self-taps into the plastic. The other goes through to the nut and provides clamping pressure.Assemble as shown, fit on the rod. You have to bend the sensor transistor so that the face of the transistor is facing where the magnet will be. Move the sensor up to the motor mount and mark the location of the sensor.The correct pole of the magnet must face the sensor. Power up the sensor and determine which side of the magnet makes the LED light when brought near. Mark that side with a felt pen. Glue the magnet in the place you marked before, with the mark on the magnet facing the sensor. Once the glue sets you're ready to calibrate and print.