These simple add-on parts are for a Prusa i3 with those "z-top" parts that have a through-hole allowing the smooth rods to move up and down. Clip these onto the "z-top" parts to keep the Z smooth rods in place during printing. Remove them when you want to slide out the rods for maintenance.If you need to use/edit the SCAD file, make sure to download the zipped "data" folder and uncompress it in the same folder as the SCAD file.