Abstract: An electric motor furnished with an end flange for its attachment to the wall of a bracket or the like, includes a belt tensioning contrivance incorporated in the flange. A circular projection the center of which is parallel and eccentrically positioned to the shaft of the motor protrudes out of the end face of the flange and engages with a circular perforation of corresponding size in the bracket wall. The motor shaft extends through the perforation, and a drive pulley is fastened to it. By turning the motor about the axis of the perforation, the shaft and the pulley describe a circular path, whereby the distance between the drive pulley and a stationary driven pulley is changed, permitting ready placing and tensioning of a belt or belts running over the two pulleys.