The new MightyMount adapters are made to secure round/square bar only gear mounts to the new CoreBar and JetStream crossbars. If you are one of our long time Yakima users upgrading your ride with a new StreamLine Base Rack System, these adapters will allow you to continue using your favorite mounts. Durable and flexible nylon adapters designed specifically for CORE and JETSTREAM crossbar shapes. Allows most RoundBar style mounts to attach in minutes. Sold as a set of 4.