It is a ring form of a solenoid.

In these miniature circuit breakers, the current is run through a solenoid, and, in the event of excess current flow, the magnetic pull of the solenoid is sufficient to force open the circuit breaker's contacts (often indirectly through a tripping mechanism).

It gives me the armature for the whole thing you're going to be going through.

In 1860 an important improvement had been made by Dr. Antonio Pacinotti of Pisa who devised the first electric machine with a ring armature.

Since the current is in the opposite direction along each rail, the net magnetic field between the rails (B) is directed at right angles to the plane formed by the central axes of the rails and the armature.

I wasn't thinking about a dodo skeleton I just noticed that as I finished this skull, the armature wire that I had been used to holding it up was sticking out of the back just where a spine would be.