Summary

This endstop is intended to use with optical endstop. It uses z-axis 6-mm smooth rod as a support and as a sliding guide, but may be mounted on it without any disassembling of a printer structure.I's adjusted with a single screw.

Instructions

Print it.
Screw an optical endstop to top (larger one) part with two M3x20 screes and nuts. It's recommended to use an optical sensor with a photo-diode slit, parallel to the board. Using sensor with photo-diode slit, perpendicular to the board, will dramaticaly reduce the precision.
Click both parts on the rod. Use two M3x25 screws with nuts to slightly fix both parts on the rod
Use M3x30 screw (hex-slot is preferred), nut and a spring to assemble adjusting system. Spring, taken from ballpen, usually goes well.
Make a flag from a tin-plate and glue it to Z-axis movable part, or use printable flag.
Preadjust the endstop and fix the lower part by tightening it's screew.
Use it. It's not required to fix upper (movable part) by tightening the screw.

Yet another huxley adjustable Z-endstop