The part is a grommet and there is a flange, or should be on the outside where the nipple passes through the rim, and inside where the nipple seats. Sounds like you broke a grommet and what you saw was the half on the outside of the rim. The other part is either still around the nipple, stuck to your rim liner, or getting ready to flat your tube. I just had the same thing happen, but several grommets were failing at once on my old rim. My LBS said replace the rim, although several members here say that you may be able to use a nipple washer to help keep the nipple from eating up the inside of the rim. I would take it to a reputable shop and let their wheel builder give it a look. If one grommet has failed, others are probably not far behind. Maintenance now could save your rim.
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Originally Posted by
colorider
Phobias are for irrational fears. Fear of junk ripping badgers is perfectly rational. Those things are nasty.