Abstract: A clamping device for clamping to a parallel sided support, e.g. a desk top or shelf comprises an elongate base on which is rigidly mounted a first arm. A second arm is slidable on the base and carries a screw which engages the rear face of the base to define a pivot axis. A second screw is manually rotatable to engage the base and pivot the arm about the pivot axis until the edge of the face plate engages the base to lock the arm in position. By suitable pre-setting of the screw the arm locks when the face plates are parallel. The clamping device may be used to support a microfilm projector.