These option parts are strengthened versions of the B parts from Item 53602. The carbon reinforced molded polycarbonate parts offer increased strength. They are particularly useful for frequent towing. You can expect better axle shape retention and gear durability when using this reinforced part. Carbon Reinforced Matte Finish Axle x2Compatible with Items 56302, 56306 & 56333.If using with Item 56310, only parts B1, B6, B13 & B14 are compatible.Not compatible with Tractor Trucks or Carson Trailers.