1/2" NPT Hex Nut

thingiverse

In making rain barrels, I found I was getting leaks around the 1/2" NPT fittings (even though they were tapped and sealed) when things would warm-up in the sun. I decided the thin walls of the barrels weren't enough to keep things tight. So I hacked this up, printed them in Nylon, and screwed them onto the fittings inside the barrels and slathered some flexible sealant around them. No more leaks!