I had a large amount of 2020 extrusion on hand and I needed 2040 so I decided that instead of buying 2040 extrusion I would just use a coupler and some covers for added strength and it worked. There are 4 different types of couplers 2 with no tolerance and 2 with .1mm of tolerance as well as two different types of couplers for different extrusion profiles. Depending on the length of the extrusion you are using you might need multiple of these along the interior. They are suprisingly strong and if you have any ideas for improvements or if your specific extrusion is different than the two that I have please feel free to remix and add to what I have. I haven't done ABS but I found that I didnt really need it so I stayed with PLA