The optical reduction of openings (12) in insulating housings (2) of terminal blocks (1) and an external characterization (23) of said series terminals, is achieved by terminal blocks being provided with conductor connection elements (4). The respective actuating opening of each contact point, which is used to receive actuating tools, is closed by means of a flap (17) provided with an integral hinge, the flaps forming a common surface with the insulated housing. Said flaps can include a visible feature or indicia on the surface thereof, characterizing the type of connection element.