This is a 150 to 120mm Bright Tangerine Clamp-On Ring for Bright Tangerine Viv and Viv 5" matte boxes, it allows you to clamp your matte box to the front of your lens with a 120mm front outer diameter. The ring features a split design allowing for gentle compression that holds your matte box securely on your lens. This allows you to mount your matte box on your lens without needing to use support rods.
The ring features Z-cuts, which allow it to compress and grip the lens securely, so your matte box does not fall off. The Z-cuts also prevent light from behind the lens from reflecting of any filter and degrading your image.