I just got a set of unused MG factory bar end mirrors that came on the V7 Racer 10th anniversary / Stone S bikes.
I've got all the parts (I checked on the exploded parts diagram).
When I put everything together, the mirror arms are quite tight on the bar end, but you can move them back and forth fairly easily. I can't see how these would tighten down anyfurther as there is no screw to snug them as most of the tension seems to be coming from the bar end.
Does anyone have these mirrors on their bike and are you able to move the arms back and forth?