Harbor Freight, US General Utility Shelf Unit Tube Extensions

I wanted shelves to put the many boxes of filament without wasted space. I used two, four tier U.S. General units from Harbor Freight Tools but wanted each shelf height to be between eight and nine inches. Most of the original tubes I just cut off to the desired length. I used the cut off pieces (8) to make four new tubes. The printed joining pieces tap in with a mallet. No supports needed, the 90-degree overhang may have a string or two to cut off but once put together it looks fine. 

I also wanted a slender shelf height at the top. I made eight inserts and used 1" PVC cold water pipe from a big box hardware store to make the top shelf tubes. Those printed pieces should slip into place without a press fit. I painted the PVC with flat black spray paint. They are very thin, take care not to put much force on them. If you hear one crack it's not going anywhere being nearly bottomed out in the hole. Since it is not the strongest section, I would suggest using it for the top shelf.  I now have eight shelves a little over six feet tall.
Used black PLA, 0.20 layer, 30% infill, 3-layer walls.