12"/30.5cm Double 1&rdquo;Ball Arm, Aluminum Alloy Medium Length Arm, Joint Underwater Strobe/Video Arm for Underwater 1&rdquo;Ball Joint Arm Strobe and Lighting Systems Construction: Corrosion-resistant aluminum alloy Length: 12"/30.5cm Weight: 100g / 3.5 OZ Ball size: 1"/25mm Package includes: 1 x 12"/30.5cm Double one inch ball arm