SnowCruiser NEW NASA type Locking Adapter Mounting System (6003) - (Fix Clip 21mm) ALL NEW "NASA type" Locking system for greater safety, ease of use and durability. Auto-Locking feature is standard on all SnowCruisers products for incomparable safety and easy of attaching and detaching. All parts are replaceable, reusable and recyclable for years of use. Can replace and use with Spikes-Spider products Compact, Sports, Alpine Pro series. Greatly reduce vibrations, increase stability and easier to use in cold and snowy situation.