Half-round spool arm adapter for LulzBot TAZ5

I kept looking at how the stock spool arm for the LulzBot TAZ5 seemed like it was the wrong shape and would cause excess drag (being square while the spools are all round).
So I did a quick design in Blender and created a spool arm adapter that just sits on top of the existing arm - no need to replace the arm at all.

The first pass didn't include the extra ridge on it and the spool had a tendency to slide all the way up against the frame. The addition of the ridge keeps the spool nicely in