This is a bit holder for the Milwaukee M18 hammer drill model 2904. It screws to the same spot where the belt clip is screwed with #6-32 screws. I printed it in PC with a 0.8 nozzle and 1.2 mm extrusion width to make it stronger, but PLA and smaller extrusion widths should work as well.
The author marked this model as their own original creation.