Top picture shows the two styles of ordinary none dipping mirror. Bottom picture shows two types of dipping mirror.
I picked another ordinary rear view mirror off eBay. Much to my surprise the fitting it different.
The stem ends in a female socket rather than a male ball (rightside of 1st picture) : the mirror has a ball on a stalk on back.
Now I can fit the dipping mirror I already have onto this new stem.
Job done!
Thanks for David Pearson of Canley Classics for taking the time to try to help. Problem now sorted. I never thought that there would be so many
variations on a theme. I would have thought that Stanpart tried to standardise!