I have confirmed that there is no such item available from either 80/20, nor Faztech (compatible) for joining parallel extrusions. You could use a butt-joiner, but that is not as ideal for these "parallel" scenarios. I actually need this for joining long 1530 and 40-4096 pieces together. This works with any 15 or 40 series extrusions great!
I also created a hidden bottom/inside 90 degree corner adapter to complement the existing 2 bolt top/inside 90 degree corner adapter (they don't make one like this).
I printed these with ABS at 50% infill and they fit perfectly, which is to say snugly, may need to tap a little with a mallet to make slide in some pieces, but no breakage.
1515_joiner_best.stl | 5.4KB | |
1515_joiner_bottom_90.stl | 20.8KB |