Interfit speed rings are designed for use with Interfit's line of professional softboxes, as well as with various other brands. The rings are made out of high-quality metals to ensure stability. The outer diameter of these speed rings is a standard 19cm (7.5"), making it compatible with thousands of softboxes from dozens of manufacturers. The inner rings on these speed rings have a diameter of 14.5cm (5.8") and can be changed out to fit any manufacturers light (inner speed ring adapter required). This speed ring is designed for use with any light that uses the Profoto mount.