It's a buttplug for my Air plug for my air mattress. 3 of them actually! So recently I was going through my 
dolls camping stuff, and was surveying what I need for camping at the end of the month.
The good news... I have plenty of air mattresses
The bad news... none of them can hold air
They were literally all missing their plugs. What good is an "air mattress" if you can't keep her it inflated??
Initially I looked online to see how much they were going to be to replace... at $5-15 shipped. TIMES 3... I couldn't justify ordering them... and then have them possibly not work.
Luckily, I have my handy dandy 3d printer. One quick search on thingiverse.com led me to this very link and HUZZAH.
After a relatively quick test print, I was able to verify it threaded properly, and was in solid condition. With this model I set the supports at 70 degrees so it didn't gum up the threads, but still supported the cross section for making the 1 way valve.
Unfortunately, you can't really just print a 1 way valve so I took of my nerd hat, and...
With some...
.... I was able to make a very cheap, nearly free, working 1 way valve to add to my very cheap, nearly free 3d printed plug for my SDCC exclusive air mattress.
