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Dear advisor,

I am going to change my plugs soon to iridium ones. The picture on the box shows step 1 as hand tightening the new plug. Step 2 says " M12:1/2 ", with a picture that shows tightening with a wrench by about 50 degrees. Please could you explain what M12:1/2 means? Do I tighten by what seems to be about 50 degrees? (I took a photo of the picture but it cannot be copied onto this email).

Many thanks for your valuable advice.

Cheers.
Leo

Without seeing the context of the M12:1/2 you refer to, I'm not entirely sure what's being referred to, however it's perhaps part of a table saying that 12mm plugs should be tightenned a further 1/2 a turn once they are finger tight - which would generally be about right.
Otherwise you can use a torque wrench if you can obtain the correct torque setting. Basically, the biggest danger if you're not familiar with the "feel" of getting a spark plug tightenned correctly is that you'll over-tighten them, which can damage the thread in the cylinder head if you're not careful.
Maybe, if you're not sure about this, get your mechanic to fit them.