5.5mm Stem Diameter fits both Intake and Exhaust - BC premium valve guides feature a threaded end where the valve stem seal goes, virtually eliminating the seal popping off at extended rpm's. Made from Manganese Silicon Aluminum Bronze alloy and CNC machined to exacting tolerances. BC guides are resistant to cracking and corrosion, while reducing friction and insures high lubrication even at elevated engine temperatures and rpm's. The perfect replacement to worn or damaged guides and 100% compatible with BC's lineup of stainless steel valves (set/8).