The threaded post that sticks up from the lower burr assembly is simply a 10-24 x 1.25" stainless screw with the edges of the head ground flat. It's function is to lightly stir the beans at the entrance to the grind chamber preventing the beans from jamming together and blocking the grind chamber. Approximately 1/4" of the screw is threaded into the lower burr support. The screw is locked into place by a jamb nut with an external tooth lock washer. Any reasonably competent handyman should be able to make this part with a grinder and some files. Another option may be the local vocational school if they have a tool and die program. I would definitely use a stainless steel screw for safety since much of the common mild steel hardware may be cadmium plated.
1 hour ago