Aquatec AQHB100 Tank Banger. Makes sound signal underwater to get your diving buddy's attention. Made of elastic stretchy rubber that can be stretched to 2 times longer, suitable for 12-14L tank. Flexible loop which allows the banger to hit the tank effectively. Simple, reliable and long lasting, easy to use. Material: PVC. Loop Perimeter: Approx. 45cm /17.72inch. Ball: Approx. 3.3 x 3.6cm /1.30 x 1.42inch.