I think that there are a few things that make it less likely to be a terret ring - and thus for coach or chariot
Most terret rings have smaller loops at the base instead of pins. The few pins I have seen are iron inserted into the bronze base.
The actual pin on yours that fastened it to something is quite thin. You can see the the broken bronze pin is about 1/3 the diameter
of the whole base. I think that terret rings were stronger.
Also this form of the base and pin looks like stuff used on Roman
furniture - though admittedly I can't find a parallel for the big top loopy bit
Yes, metal was expensive but high end Roman
furniture used lots and lots of metal as display. You can find museum examples with big carven figures, chair legs entirely fronted with thick bronze, etc.
Overall it still
goes in the uncertain for me...