The SunwayFoto DDC-26 Screw-Knob Clamp is an all-metal, Arca-swiss style clamp that attaches to tripod heads via its 1/4"-20 mounting hole and included 5mm screw. Its jaw opens with a range of 38- 41.5 mm and its captive-design knob locks tightly to secure your camera. Designed with a "+" shaped mounting groove on the bottom, its orientation can be changed to fit quick release plates set in either direction and it can be perpendicularly attached to a second DDC-26 and used on a rail mount. Two safety relief grooves help to keep your camera secure.