This is a WORK IN PROGRESS. It's a mount for an inductive NPN sensor with an M8 threaded shaft like the "Finglei Electric LJ8A3-2-Z/BX-5V" I'm planning to use to a chinese 4th axis containing a 50:1 harmonic drive. There are 2 versions of this gear box. With 6 and with 4 mounting slots. The sensor holder was designed to fit both. (Technical drawing will follow, after I have tested the sensor.) Update: In MK2 I forgot to leave clearance for the heads of the M6x30 machine bolts. So I had to change the design slightly for MK3. Blog posting: http://marcuswolschon.blogspot.de/2016/12/adding-homing-sensor-to-4th-axis-on-cnc.html