My nephew got a bicycle for his birthday which means I had to print him some Darth Vader tire caps for his almost all black mountain bike.
I believe it's a Schrader valve.
I did up the file to 105% in my slicer that seemed to fit the best.
I remixed the Lego Darth Vader head with a Tire Valve Stem Cap.
I was inspired by the Storm Trooper one but had black PLA filament loaded (https://www.thingiverse.com/thing:40873)
Also, I didn't realize until after I remixed and printed my file that there was already a Darth Vader Cap (https://www.thingiverse.com/thing:1008313) I would have just used that.