This lever is used to adjust the clamp on the Arca Spec mounts, the pan/swivel, and cant motion on G2 and current bipods.
For instructions on how to swap and maneuver the lever, please watch this video.
DO NOT TIGHTEN WITH A TOOL OR ALLEN WRENCH! This lever is adjustable. If you hit a stop and the tension is not where you desire, pull the lever toward you, reposition, and tighten.