An adjustable spanner wrench (commonly referred to as an adjustable wrench or crescent wrench) is a versatile, hand-held mechanical tool designed to tighten or loosen fasteners, nuts, and bolts of varying sizes. Its technical architecture consists of a solid, high-tensile forged steel handle that integrates a fixed jaw at its head and a machined guide track. A movable jaw slides smoothly along this track, regulated by an embedded, threaded steel worm screw (knurl) that engages a gear rack on the underside of the sliding jaw. This configuration allows the user to infinitely adjust the jaw width within its maximum opening capacity, eliminating the need for multiple fixed-size wrenches.

Operation relies on manual torque application and simple mechanical adjustment to securely grip a fastener. To use the tool, the operator rotates the thumb-operated worm screw to open the jaws, places the wrench over the flats of the nut or bolt, and tightens the screw until both jaws make tight, flush contact with the fastener’s surfaces. To maximize leverage and prevent structural damage to the tool, the wrench should always be pulled so that the rotational force is directed toward the side with the movable jaw, ensuring the heavier, fixed jaw bears the brunt of the load. Once the fastener is rotated to the desired tightness or loosened completely, the worm screw is backed off slightly to release the grip.