Abstract: A tightness control or discriminator for a double seam between an end unit and a container body. The tightness of the double seam is proportional to the force required to form the same in the second forming operation, and this force is reflected in the pressure engagement between the associated cam follower and second operation seaming cam. A load sensor is placed within the seaming cam adjacent the reaction surface thereof for varying of its electrical resistance characteristics in accordance with the seaming force and there are suitable devices provided for indicating, either visually or by way of an alarm, the reaction force which is indicative of tightness.