Raw brass "settings" (not really settings as there's no indentation or cup to hold a cabochon in position).
The size was measured inside the lacy edges. Shown in one of the small photos with a 25x18mm cabochon.
Also shown in 2 photos wrapped with Rhinestone Chain (as an accent and
to fill in space on mismatched settings).
I'd suggest G-S Hypo Cement or Zap Gel Fill-In Glue for adhering the
cabs to settings.