Abstract: A C-shaped brace member threadedly receives a screw shaft and supports a channel-shaped die. The lower end of the screw shaft is connected by a ball and socket joint to a pair of hinged pressure plates positioned in parallel relation with the opposite walls of the channel-shaped die. Rotation of the screw shaft in a preselected direction raises and lowers the shaft to extend and retract the pressure plates toward and away from the walls of the base member. An end portion of a gutter section to be expanded is positioned on the base member between the longitudinal edges of the pressure plates and the walls of the base member. Downward movement of the screw shaft moves the pressure plates outwardly toward the walls of the gutter section. The pressure plates contact the walls of the gutter section and bend the walls outwardly to expand the width of the gutter section until further expansion is restrained by the walls of the base member.