Mfr # 820.4-355-PL. GN 820.4 horizontal acting toggle clamps have a safety function whereby, during closing, a spring loaded safety hook latch ensures a secure locking connection. It prevents the inadvertent unlocking of the clamp due to vibrations or an accidental attempt of loosening / opening of the clamp. To open and release the clamp, pull up on the finger grip to disengage the safety hook latch mechanism (one hand operation). They work according to the toggle principle: lever and clamping bar move in the opposite direction. They require less space for the clamping action.