Without mounting the motherboard sheet across the front of the Mendel, the frame flexes too much when printing at high speed. These braces should fit snugly over the threaded rods to stiffen the frame. Slots for tie wraps are provided if needed. Paper can also be used as shim to make a tight fit if needed. Two might be enough but I printed four (see STL file with all four pieces laid out) to be sure.