This optical endstop holder is used for a precise adjustment of the z-axis. The basic idea of the endstop fixture is from Prusa's Mendel project (endstop-holder.scad). https://github.com/prusajr/PrusaMendelThe basic idea of the vertical adjustment is similar to "Vertical Adjustable Opto Z Endstop Holder" from LittleDangerous http://www.thingiverse.com/thing:23858 Adjust the size parameters in the scad file for your printer and print it. Or you can just use those uploaded files for printing: 1 x VzE_wheelV2.stl, 1 x VzE_holderV2.stl, 1 x VzE_endstopV2.stl1 x springs 5.4 mm x 17.5 mm 7 x M3 nuts 1 x 35 mm M3 HexBolt (total threaded) 1 x 40 mm M3 HexBolt (half threaded, half smooth) 1 x 20 mm M3 HexBolt 2 x 15 mm M3 HexBolts 5 x M3 washers Take the 40 mm HexBolt and decapitate the bolt's head - not your finger! There are several ways how to assemble it, but lets describe my way. Drill the holes of the endstop-part for some time using a 3.0 mm driller. The bolt must slide very smooth through these holes. It will also work with a 3.2 mm hole, but then the holder will shake a little bit. Secure both bolts as shown with nuts on the holder part. You need the spring above the thumb wheel on the black bolt. Use grease on the other long silver guiding bolt. Put 2 washers above the thumb wheel. The thumb wheel's nut is pointing towards end of the bolt. Make sure both bolts are parallel and the spring is not interfering with the threaded bolt. The last photo (V1.0) shows how to assemble it without cutting a bolt's head.Version 2.1 Version 1.0