A fixture includes an elongated rod, a first jaw and a second jaw. The first jaw and the second jaw are assembled with the elongated rod. The second jaw has a pivotal portion and a grip. A trigger is connected outside the pivotal portion. A front chamber is formed in the pivotal portion for receiving a plurality of clasping pieces and a restoring spring penetrated by the elongated rod. The restoring spring pushes the clasping pieces to synchronously drive a push rod connected to the trigger. Each of the clasping pieces is formed with a groove facing the restoring spring. The restoring spring is formed with a guiding section bent toward the clasping pieces. The guiding section is disposed in the groove to guide the second jaw to advance smoothly.