My wife and her sister are homeschooling our children. Thanks pandemic! To teach the kids about various aspects of science they had taped two soda bottles together with water in one side. And you know what I said? "I should print you a double-sided cap."

And so I did...

Like any good engineer, I didn't want to reinvent the wheel so I looked for a bottle cap to modify. I found the really nicely made Bottle Cap PCO 1820 Cap and Neck with standard thread by bramesh501 and I Remixed theirs. Thanks bramesh501!

Initially I mirrored the source but that ended up reversing the bottom threading. Whoops. Fixed that, and printed v 2.0. It worked! Two problems, though; It was really tight to screw on and once one of my kids flipped it 10-15 times the piece snapped in half.

Back to the Blender board...

I made this new one quite a bit thicker and I scaled up the inner diameter by 1-2 metric hairs. I also striated the outside. I loved the original model's hatching but I figured striations would give optimal grip and provide additional strength to the piece.

v 3.0 is pretty perfect!

• It is incredibly tough.
• It screwed on with ease, yet still feels pretty tight.
• I love the feel of the striations and they really do help.

If you have any ideas for improvement, let me know. I'd be happy to hear your feedback.