That's good!
So I looks at my red baron wing-capper. The crown head isn't removable.
However I looked at the metal plates that grip the neck and interestingly enough they are stamped 26mm and 29mm and are reversible apparently.
A decent tug with the vice grips and they slide out fairly easily.
Tried an old Leifmanns cap that's full of dried epoxy and it fits partway into the crown head. Wish I had one to try on a bottle itself.
Any ideas about this?