They work according to the toggle principle: lever and clamping bar move in the same direction.4 vertical acting toggle clamps have a safety function whereby, during closing, a spring loaded safety hook arm ensures a secure locking connection.4-230-BL-NI Vertical Toggle Clamp In the clamped position the operating lever is in its vertical position. To open and release the toggle clamp from the locked closed position, press the lever arm and safety hook lever arm together (one hand operation).