On my RS200, and I assume most front drum-braked '70s/'80s bikes that used the same front brake lever, the righhand mirror has a lefthand thread and the lefthand mirror has a conventional righthand thread.

What's going on here then? Anyone know the reason for this? It can't be so that wind pressure at speed does not unscrew them, as they both have the wrong handed thread for that, so what can be the design reason for this?

It buggers me up a bit as I have a very nice pair of chromed mirrors to put on the bike, but both have righthand threads. I think it's going to be a case of drilling, sleeving and recutting a righthand thread in the righthand brake lever.

Hi PB1

Before I drilled and tapped a new thread in the original mount, Try a bicycle shop and buy a handle bar mirror clamp it probably won't cost much,

My DT mirror is mounted using one of these i had lying around and it don't look too bad.

it helps them to not shear off in a fall

you can get adapters to fit them. M&P (Busters) do them I think.

As Airhead has said if the mirror hits something when you're moving forward they are supposed to unscrew rather then shear off and ruin the mounting.

http://www.ebay.co.uk/itm/Chrome-Mirror-Adaptor-allows-10mm-mirror-to-fit-Yamaha-/350286698491?pt=UK_Motorcycle_Parts&hash=item518eb6d7fb

Ah.... I understand now. Thanks for the replies and the link guys.