Neewer Aluminum Screw Knob Clamp Arca Swiss Compatible Mini Quick Release Clamp for QR Plate (38mm) CNC precision machining, surface anode anti-oxidation treatment, the body and washer is made of aluminium alloy and copper. Compatible with all AS quick release plate , such as RRS / ARCA-SWISS / KIRK / Wimberley / MARKINS / SUNWAYFOTO / kangrinpoche / BENRO / SIRUI etc. When loose the screw, you can adjust the width of clamp. Material: Aluminium Alloy, Copper Mounting Thread: 1/4"