Bluenet 6pcs Fluorescence Stick / Electronic LED Flash Bracelet / Light-emitting Bracelet (6pc) random color External diameter8.5cm(3.35") Internal diameters6.5cm(2.56") Replace batteries ( 3*AG3 ) Batteries are replaceable with a long battery life (ON/OFF switch) Made of hard, durable plastic that diassembles to get onto larger wrists.