Nocturnal Lights 12 Aluminum Ball Joint Underwater Strobe / Video Arm for Underwater Ball Joint Arm Strobe and Lighting SystemsThis Nocturnal Lights Aluminum Double Ball Joint Arm Section is a 12" section used to join with other components of the Nocturnal Lights ball joint arm system. Use a Nocturnal Lights ball joint clamp to join with other sections. The arm is constructed from light but sturdy anodized aluminum. The 1" ball has an o ring; this helps the clamp to hold the section in position without slipping.