That little hook attached to some tray table knobs is actually a coat hook, Lifehacker points out. Of course, it works for hanging items like earphones and sweaters, too.
On some plane seats, you’ll find the coat hook next to your tray table or on the side of the seat instead. Others have an older version that looks like a basic knob but still does the trick.
Whether or not a plane has a coat hook is a matter of airline preference.
You see, airlines order their planes from manufacturers like Boeing, then customize the interiors with the help of companies like Rockwell Collins, which manufactures airplane seats. Indeed, that tray table hook is “a coat hook option that some airlines take” when designing their cabins, a spokeswoman for Rockwell Collins told HuffPost.
The more you know.
CORRECTION: That last photo does, in fact, have a coat hook. We initially said it doesn’t; it’s an older version, and not very coat hook-y, but it is there.