This a little case that holds a fiber-optic bundle, a standard 5mm LED, and a CR2032 coin cell battery. From Chapter 4: Fiber-Optic Fabric Scarf from our book [Make It, Wear It: Wearable Electronics for Makers, Crafters, and Cosplayers](https://www.ampedatelier.com/make-it-wear-it). If you make one and post on social meda tag it with **#makeitwearitbook** so we can see it!