G7th Capos employ a wrap-spring clutch that consists of just 3 elements: a fixed hub, a moving hub, and a spring whose inside diameter is just slightly smaller than the outside diameter of the 2 hubs. When the spring is forced over the 2 hubs, attempting to rotate in the direction which opens the capo wraps it down tightly on the hubs, positively engaging them.
Rotation in the other direction, to tighten the G7th Capo onto the strings, is not restricted. To release the capo, the control tang is moved in the direction to unwind the spring, thus releasing the clutch.
The beauty of this type of clutch for use in a guitar capo is that it can be adjusted in tiny increments. The clutch mechanism is a modified tried-and-tested design used in printers and copiers to provide a simple decoupling and overrun device.