My new-to-me Bonneville arrived with a single Mickey Mouse mirror (photo). I have been searching for a matching or close replacement for the right side, and I think this model year has unique mounts. The socket is stepped in size with 15mm I.D. at the top, 11.5mm I.D. and then 10mm I.D. at the base (visible in photo). The total depth of the socket is 23mm. Can anyone point towards a potential replacement source? Thanks in advance.
As you've been a member for a while, it might be an idea to post your request here. https://www.thetriumphforum.com/forums/wanted.24/
That looks like a standard Bonneville mirror. They aren't threaded but fit on a taper with a serrated ring. To get an idea of the fittings have a look on one of the parts diagrams on line, such as on www.worldoftriumph.co.uk or www.fowlersparts.co.uk.
I have a RH one that should match, unfortunately there are a couple of scratches on the back of it. I also have a pair of the oblong ones but once again the RH one has scratches on the back. It would appear that the PO was fond of dropping the bike on that side!