I would go with 12mm, anything much less is liable to bend if you hit a brick or whatever as you're whacking it in. You probably know, but it comes in 3m lengths.
Cheers.
I didn't realise it came in 3m, but the closest seller to me on ebay cuts to the m for an acceptable price.
@hugo7 started
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I would go with 12mm, anything much less is liable to bend if you hit a brick or whatever as you're whacking it in. You probably know, but it comes in 3m lengths.