I found this strange looking bit in a bit set of uncommon bits, including Security Torx, hexalobular, tri-wing, spanner head, 12-point flange, Torq-set and others. It's the only one that I could not identify, what is it for?
My first thought is that it might be intended to be a wing nut driver of some sort, but those are usually hollow cylinders with slots for the wings.
Ah ... sure enough, it's described as such in this Ebay ad:
There is one sold on Amazon.com, an "Eazypower 80935 1/4 inch Y-Shape Cup Hook Installer and Remover". https://www.amazon.com/Eazypower-80935-4inch-Installer-Remover/dp/B000PSABL0
I usually use a pair of pliers to screw hooks in or out. Quite honestly, I like the wing nut driver idea better.