Southco it is
Thanks for the lead.
Discovered they are close to their number E3-15-17, but due to the age cannot confirm.
They are $38.00 each and the company advises they are not field serviceable, I will need to remove one to see if that is so.
If not I may drill small holes in the flat and create a different way, I have security drivers that use 2 or 3 pins to drive, not as good as the ring, but better than nothing.
May also look at spinning up the lath and creating a fixture to allow for drilling of the holes in the bottom so the surface is still flat, more difficult but security remains same.