This is a coiled, 17.8" Fiber-Optic Cable II from Sea & Sea for use in underwater photography. It's equipped with two 90° Sea & Sea fittings on the ends; one connects to a compatible external strobe, and the other connects to the fiber-optic cable socket on select underwater housings, allowing your strobe to be triggered by the firing of the camera's built-in flash. It's compatible with all Sea & Sea housings and strobes and is designed for use with the internal Optical YS-Converter. Since the cable is bi-directional, either end may be attached to a housing or strobe. The cable is composed of 613 fibers, or cores, as opposed to one large fiber, to ensure that light transmission remains high even when the cable is bent, and also to increase durability and resist bending.