Abstract: An automatically adjustable locking pliers includes an upper jaw fixed to a handle and lower jaws that pivot about the handle. The lower jaws are connected to a lower tightening handle. A lever connects the tightening handle and upper body. This is the standard structure of locking pliers well known in the industry. The improvement includes a self-adjusting sizing and locking mechanism A thumb jaw sizing lever is located near the jaws and may be moved to open the jaws so that they can be sized around a workpiece. When the thumb jaw lever is released, the jaws automatically size and clamp lightly around the workpiece. The sizing lever and locking mechanism operate together to automatically size and lock the pliers. An adjusting screw in the lower handle near a pivot point sets the clamping force. Turning the screw adjusts the tension of the pliers for gripping the workpiece.