Pursuestar Baby Rotary Mobile Crib Bed Bell Toy Windup Clockwork Movement Music Box with Rotating Hook - Brahms Lullaby Dimension: approx. 12cm*7cm*3cm(4.72"*2.75"*1.18") Material: Eco-Friendly ABS and metal music movement inside How to use: the sound power from spring, use the key to turn the spring tightly, then release and will be playing Playing speed: 12-20"; Full playing time: 2-3 minutes; Service life: &gt;=500 times No batteries required, windup movement inside, safe and environmental friendly.