These clips are most commonly used to sew hair extension tracks to them, then used as clip-in extensions. They are also used to anchor wigs down to a talents natural hair.

These come in 4 colors:
Black
Brown
Blonde
Silver

Sizes are shown below:
Small: 5/8"
Medium: 1 1/8"
Large: 1 1/4"
Extra Large: 1 3/8"