These had many uses back then. They helped button up boots, hook-up corsets and helped button all those tiny buttons on things back then.
This is pearly celluloid (not Bakelite). Hook appears to be steel.
Nowadays? I'm sur there are plenty of uses but this is a great decorative / display item for a vanity. If you see the last photo, you will see the vanity filling up with items already listed! Most of Luna's home items are vintage and antique vanity decor.

This item is sold from an excellent, highly rated vintage boutique in Northfield, OH.