Prusa i3 Snap-on Y endstop bracket.

Snaps on to the smooth rod and threaded rod, assuming they are close to 21mm apart. Can be mounted on left or right side. You may need to lower or raise your bed to ensure it hits the end stop. Because the end stop is in a fixed position you'll no longer have to worry about missing if it's rotated or any of that nonsense. Notched at the bottom to leave room for a nut on the threaded rod. Works with standard Makerbot mechanical end stops.