Ordered these with a Sting Ray Hydrofoil and they are not worth much. Very bad design. Each is attached by a single sheetmetal type screw which fits into a unthreaded boss molded into the fin. One of the fins was split by the screw when installed. I returned both to to the company and they replaced the item, but took 4 months to do so. They do not appear to have been improved and I will probably not install them. I would not buy a String Ray product again.