Abstract: End caps for printing substrate rolls that are configured to engage with a print roll retaining mechanism of a printer in order to regulate total web tension of a printing substrate during a printing operation are shown and described. Each of the end caps has a cylindrical body including an attachment mechanism for attaching the end cap to the printing substrate roll; a continuously curved outer wall longitudinally aligned with the cylindrical body and configured to define a first component of the total web tension; and a central protuberance that is concentric with the continuously curved outer wall and longitudinally aligned with the cylindrical body, an outer face of the central protuberance being extended beyond an outer lip edge of the curved outer wall, the central protuberance configured to define a second component of the total web tension.