Three way connector with a peep hole. Corner piece for three orthogonal rods in a grow tent. STL file for rod OD = 20 mm.
OpenSCAD file included for your adjustments.

Print instructions

Print this thing standing on the corner (peep hole) with a small brim.

I added an optional plug to close the peep hole.

… and we were told to recommend fixing the rods with screws, for example like this:

Take a look at our grow tent:
https://www.printables.com/model/106703