A fixed mount for 2020 extrusion allowing any length to be fixed. This uses the already tapped holes on the Prusa MK3 (M3 thread).
The 2020 extrusion can be fixed in place by 1-4x M5x14mm machine screws, depending on how much weight it needs to support. The bolts are primarily used for fixing in place, and do not support the weight of the arm, the design of this print handles all the load.
The author hasn't provided the model origin yet.