Toggle Principle:

Toggle action clamps operate through a linkage system of levers and pivots. The fixed length levers, connected by pivot pins supply the action and clamping force. Toggle action has an over center lock point which is a fixed stop and linkage. Once in the over center position, the clamp cannot move or unlock unless the linkage is moved. All types of toggle clamps have same action, just oriented differently.

The Toggle Mechanism in a clamp has three functions:

1) To multiply applied load at the handle into a high clamping force to hold the work piece.
2) To create an over - center lock to prevent the clamp from opening & releasing the work piece
until opened by the operator.
3) To rapidly open & close the clamp giving a maximum clearance in which to load & unload the work piece.