I have been finding it difficult to adjust the Z axis end stop on my Prusa. I am normally able to get it to the correct ball park, but getting the adjustment of the bed to extruder spacing correct was taking some time. Each time I moved the end stop up or down I would move it too far.
So I came up with this solution.
It consists of two parts, the top plate holds the opto sensor and has a cable tie to hold the wires securely. The bottom plate mounts to the machine and fastens two bolts with spring and nuts to provide tension for the top plate. A bolt with a locking nut is used to move the opto sensor up and down by small amounts.
Full assembly instructions and the OpenScad and STL file can be found here on Thingiverse.