That is half of a key ring. There is actually another half that attaches to it with another ring on the other end. The design allow you to separate the keys if needed with out having to manually turn the key around the ring to remove it.
Given the color I think it may be a "safety key" or perhaps a disconnect key.
2016 F350 6.7L LB CC Reese 28K 2014 Chaparral Lite 266sab
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