Features 1、Light Material: Made of silicone and PA66 material, which is light weight, easy to carry, durable, can be used for a long time. 2、Easy to Use: The knocker ball is easy to hold and use in underwater situation and environment, increase the possibility of being helped in special condition. 3、Using Method: Put it on a diving cylinder, pull the strap in the water, and when you let go, the ball will hit the tank with a loud sound, making you easier to be heared by your partner or others. 4、High Elasticity: Strap part has high elasticity, that the hitting ball can be used on most cylinders of different sizes. 5、Much Louder: Set on your diving cylinder, pull the ball, it makes a much louder sound than other diving equipment, practical diving accessories. Item Type: Diving Cylinder Knocker Ball Material: Silicone + PA66 Application: For Underwater Signal, Outdoor Sport Weight: Approx.37g/1.3oz Package List 1 x Diving Cylinder Knocker Ball