What a load of techy's you lot are turning out to be .....
Just been out to check mine, 4mm allen key, must be an M5 bolt
Mine was so rusty that it was hard to tell. I did manage to get them out and remove the mirrors and yes - correctomundo - they are an M5 x20
For those who haven't looked at how the mirror fits on the ball it's quite simple.
The base of the mirror is one half of a socket and a metal bracket is the other half. The bracket sits and pivots on two 'knees' which rest in a couple of square holes on the opposite side of the M5 Allen bolt. Tightening the bolt clamps the mirror and the bracket on the ball. To tight and you can't swivel the mirror, to loose and the mirror will flop about in the wind.
The original bracket is plastic coated by the look of it, although the coating fell off when I removed mine. After attacking it with a wire brush I dipped the bracket in a tin of Hammerite and after drying for 24 hours reassembled and put back on the ball.
I'll be replacing the bolts with some stainless ones when the arrive as if they seize up or snap off it'll be new mirror time ...
Very comprehensive
If you have some ASP (Anti-Scuff-Paste) or similar
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