Description Reviews Supertech Valve Guides are precision-machined from high quality Magnesium Bronze material. These guides will fit the intake & exhaust the MINI Cooper & Mini Cooper S (R50, R52, R53). They will fit a 6mm valve stem. Pair these in combination with low friction nitrated valves to provide the best solution for performance and durability. Also don't forget to add valve springs and vales seals! Note: Sold as a set of 8. You will need 2 packs to do all 16 valves.