I use this as a protector for the Heatbed. you need two of these and put it to the rails.
you need to adjust the z switch so that it switches on the height of the protector.
you can then also level the second side of the x-axis. i designed it because when i tried to switch to auto level the firmware crashed multiple times in the bed. You have also to adjust the bed to this new height.

you should be aware that when you run against the protector the coupler will expand. so be sure that the coupler didnt expand when the endstop is triggered