This is a refill cartridge for the Automatic Brow Pencil Duo. Snaps easily into place so you can change shades in an instant. The snap-in, snap-out cartridges let you create your own custom eye tool. For example, if you have an Automatic Brow Pencil Duo in one shade, try a refill in a second shade—or add an Automatic Eye Pencil refill for brow color and eyeliner in one.