Abstract: A screen installer's tool for use when installing screening material in a frame. The tool is designed to be held in the hand with a knife blade at one end and a rotatable screen forming wheel at the other end. The body of the tool is made in two parts joined together by screws with an internal compartment which houses a supply of knife blades and also a slidable knife blade carrier. The carrier includes a finger-operable detent and pawl for permitting slidable movement of the carrier and knife blade in and out of the internal compartment so that when not in use the knife blade is locked in place within the tool body.