The parts are for this amazing printer (Vulcanus V1, CoreXY based): http://www.thingiverse.com/thing:821066 I didn't like the way the z-endstop was clamped to the smooth Z-rod so I've build my own easy-to-level-Z-parts. You have to print my z-rodholder to screw the endstop in and my z-axis LM8UU Bolt part to put a M4 nut into it and screw a M4 screw through it. Both parts will perfectly match each other, please see the images and you'll know how to use them. If you wish you could print my M4 hex nut holder for better rotating the screw by hand. With this solution you don't have to clamp the z-endstop on a smooth rod - you can attach the z-endstop in a better way and you can adjust the z-height more better.