No matter what your likes and dislikes. You're sure to love these light up spikes. Wear some while you play your blues harp. They're made of soft rubber so the spikes aren't sharp. Each pack of 12 contains 4 different necklace colors. The necklace has two snap-buttons for desired size. To activate, remove the protective slip from within the battery housing. Then twist the canister to the right to tighten the housing to the batteries. To deactivate, simply loosen the battery housing by turning it to the left. Length: 15.75 in. , 40.0 cm. Depth: 0.62 in. , 1.57 cm. Necklaces Colors: Blue, Pink, Purple, Yellow LED Colors: 1 Blue, 4 Red, 3 Yellow Batteries: Includes 2 CR927 Batteries.