Spools permanently lock both axle shafts together so both rear tires will always turn at the same speed. Many Strange spools allow the use of larger axle splines that tremendously increase axle strength. The lighter and stronger steel spool also improves ring and pinion life by providing a more rigid gear mounting. Strange Pro Race Spools are forged with Strange designed tooling from premium steel. The forgings are machined on all critical surfaces by computer controlled machining centers and are fully heat-treated. Strange pro race spools are the lightest on the market and have lifetime replacement policy.