Simple tube to extend a shower rod.
Expected rod dimensions:
Inner diameter of 14mm, outer diameter of 16mm.

Somehow the shower rod that came with my apartment was too short, so I made this up in TinkerCAD rather than buy a new one (seriously how did that happen??)
Pennies worth of material to save me a couple bucks on a whole shower rod.

Print instructions

Honestly this thing is overkill, just print it in your favorite stuff as long as its stiff it'll be fine.