eBay

It is designed to support 5” and 7” camera monitors, which can be attached to the top of a camera cage or alternative mounting setups.
Anti-Twist Design: Bouncy locating pins further secure your device, and silicone pads protect the display from scratches and distortion.
Quickly tighten with knob to accommodate different angles.
With 3/8 1/4 screws: The bottom positioning screw connects to the camera cage, and the top screw supports monitors, microphones, lights and other equipment.
Gear bayonet, fixed more firmly and not easy to slide. Made of high quality aluminum alloy and stainless steel with strong load capacity.