Makerpipe ( https://makerpipe.com/ ) is this fun Kickstarter that makes connectors that allow you to use inexpensive EMT (Electrical Conduit) for creating things. It's kinda like having an Erector Set for adults.
I hope they plan to roll-out more connectors. I made this hinge flange that allows rotation of 180 degrees.
I've been using Makerpipe on my Solar eBike Trailer Project ( https://youtu.be/F27a7yQKD6s )
2/20/2021: I added the model of the Flange with the opposite sex hinge
The author marked this model as their own original creation.