These are for use with the MK4 Bin (two hooks) in combination with the Prusa i3 Noise Suppression Feet. When using those two together, the bin sags as it hangs from the two hooks. These feet add support for the bin. One on each bin should be enough but you can definitely use two for each bin. I printed them with 100% infill just to fill in the little holes throughout.
https://www.printables.com/model/672631-mk4-bin-two-hooks
https://www.printables.com/model/119809-prusa-i3-noise-suppression-feet
The author marked this model as their own original creation.