If you are building a 3D-printer enclosure with IKEA Lack tables, e.g. for your Prusa I3 MK3 (https://www.thingiverse.com/thing:2864118), you will experience that two IKEA lack tables do not have the same height as your standard table. Also, the floor of your room may not be perfectly flat. A third IKEA Lack table, with cut-off feet (18 cm cut-off) will bring your printer to standard table height again. These IKEA Lack adjustable feet can be plugged into the feet of your IKEA Lack table to fine-tune the height of your table.
For one foot, you need to print one "Adjustable Foot" and one "Adjustable Foot_insert". In addition, you need a M5x20 hexagon screw (ISO 4017) and the corresponding nut.