An Ultralight arm generally consists of two arm segments and three clamps giving you the greatest flexibility. Videographers sometimes use just one arm segment and two clamps.
The o-ring in the balls of the arms eliminates the metal to metal contact. This allows a much more linear clamping force, allowing you to control the arm movement when used with small or large strobes even in varying current conditions.
The ball size of this arms is 1" (25mm).