rotary solenoid

[tfkeel]

I'm looking for some education.  I understand how a push or pull solenoid works, I think.  What I would
like to know is how a rotary solenoid I have works.  I cannot figure out how the rotation is obtained.   

The coil is wound around the shaft and there is a magnetic toroid-shaped piece of metal attatched to the shaft.  Two small
metallic pieces form "stops" to keep the rotation to a desired angle.

I would understand if the shaft were pulled in to the coil center, but it does not move in this direction, only rotates.

Is there anyone who does understand its operation, or who could point me to reference material which explains rotary solenoid operation in general?

Thanks so much for your kind attention.