Abstract: An assembly tool for setting a lateral position of a rear window panel placed on a window glass support surface of a rear window opening of an automotive vehicle is provided. The tool includes an upper jaw for extending over a C pillar of the automotive vehicle, the upper jaw has a weather strip channel contact member and an adjustable length extending finger with an extreme edge window contacting surface for setting a lateral position of the rear window panel within the window glass support surfaces. A lower jaw pivotally is connected with the upper jaw for contacting and gripping an inboard surface of the vehicle C pillar. A quick connect vice mechanism for closing the upper jaw and the lower jaw toward one another to grip the C pillar is also included.