This little STAINLESS STEEL Shim Spacer is precision made. It ensures maximum performance to the wheels & nuts. Made from Marine grade stainless steel it will not rust on you! It is used to hold the bearings in the perfect position & also to bridge tiny gaps on the axles, ensuring an accurate fit with NO rattles! The Shim spacer slips onto the Axle, fitting either side of the Bearings when the wheel is being fitted onto 12mm axles. This tiny spacer positions the wheel perfectly on the axle, holding the Bearing in the best possible place to help achieve maximum spin rate for the bearing & wheel. Its little parts like these that suffer the most amount of abuse, especially when they are used in the harsh conditions that they are. Check from time to time they are in good order & possibly replacing them every now & then this good practice will ensure your board stays in tip-top condition, always!