Abstract: A tool for holding electrical boxes in position for attachment to upright studs in residential and commercial building construction. The tool comprises a main body made of an elongated tubular support member, a holder attached to the main body for releasably holding an electrical box in position for installation, a height adjuster connected to the main body for positioning the electrical box at a predetermined distance above the floor, a depth adjuster attached to the main body for positioning the electrical box at a predetermined depth relative to the face of the upright stud, and an alignment device attached to the main body for positioning the electrical box so that the sides of the box are parallel to the sides of the upright stud. One aspect of the invention provides a clamping trigger for automatic activation of the box gripping force. The clamping trigger is located and configured so that electrical boxes which are presented in misalignment do not activate the trigger.