New age, tri-compression clamp, for better grip, flexible movement and easy functioning. This clamp is used to attach two arms, base adapters, and strobe / gopro / light etc adapters together
A good arm system generally consists of one or two arm segments and two or three clamps depending on the amount of flexibility you need to achieve.
Arms come in different lengths and there are different kinds of adapters.
Ball size of all arms and adapters is 1" / 25mm
See arm segments and adapters in the arms, trays and connectors department of the underwater shop.