Steel Blue Southern Cross® Spin-FX™ Work Boot The Southern Cross® Spin-FX™ is up to the challenge. Powered by the Boa Closure System, the unique Spin-FX™ is designed to enhance performance and comfort. Made up of 49 strands of stainless steel (7 bundles of 7), braided together, injected and wrapped with nylon, the system is incredibly strong and durable. Simply spin the dial for a snug and secure fit and pull to release the wire. The precise tension adjustment alleviates pressure points, offering 100% comfort all day!