When I entered my registration number I thought you knew what you were doing,I was so wrong ,when it came up as "Recommended 6 spark plugs" so I bought only 6. When I started pulling the sparks plugs cables I noticed that my car uses 2 per cylinders= 12 spark plugs in total.I have left the old plugs for now,until I get some free time to go to an outlet to get 6 more. I took the opportunity to ask a question on line:the question I asked was "Please could you check how many spark plugs a Mercedes ml 350 3.7 w163 series year 2003 uses.A replied came back as Bosch FR8DPP33+7422+45. They never answered my question of how many plugs. I was disappointed,I never had any problem with the Staff at GSF Farnham,they have always been very helpful.We buy all our service parts from GSF as we have 4 Mercedes vehicles in the family. Many Thanks. Raouf Joommun.