Hi all. I am looking at the cam sprocket on my om603 engine. It is a 12 point bolt. The FSM says it is an M11 sized 12 point. I went to my tool box, pulled out my metric 12 point sockets send found that only a 13mm socket fits, though it is a little bit loose. So, are they different, M vs mm?

Trying to decide if I need another set of M sized sockets of if my mm ones are ok.

Thanks!

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1987 300TD named Klause
1987 300TD named Spouse
1987 300D named Seabiscuit
1980 300TD names Chloie (now sadly gone)