The self-adjusting "worm gear" has a unique "spring movable jaw mechanism" that automatically seizes a nut or bolt head.

It can also be manually adjusted by the user.

The automatic feature is activated by extending the movable jaw to its full open position.

The "worm gear" engages the jaw's rack allowing it to be secured in that position.

When the wrench jaws are placed over the nut or bolt head, the "worm gear" is then depressed (released from the rack) allowing the movable jaw to instantly seize the nut or bolt head.
The spring attached to the jaw exerts pressure on the "worm gear" as it rests in the teeth of the rack virtually eliminating the tendency for the movable jaw to “travel” during the tightening or loosening of a nut or bolt head.

Also, the worm gear can be used to give a "final tighten," if needed or desired, once the jaw engages the nut or bolt head.

THIS TRULY UNIQUE "WORM GEAR' SELF-ADJUSTING CRESCENT WRENCH
IS AN ESSENTIAL TOOL FOR EVERY TYPE OF TOOL BOX