This is the original clamp designed by Mr. Lowery and was intended to provide reinforcement for stitching frames that were nailed at the corner. However, because of the pressure (rocker plate) plate design, they are generally used VERY successfully with every type of frame, including scroll frames and plastic frames. The clamp will accommodate even VERY LARGE frames without drooping or slipping. This clamp is also wonderful or holding very SMALL canvases because the clamp can be poised away from your stitching. Please remember that CLAMP CHOICE IS A MATTER OF PERSONAL PREFERENCE.