Hi,
Actually, the magnets are in the rotor. The 50 teeths on the "gear" are alternating N/S poles of the magnets.
The stator contains the windings which, together with the iron teeths forms elctromagnets. By running current thru the windings the magnetic field developed eitther retracts or repells the magnet in the rotor. By changning the direction of current flow thru the winding the polarity of the magnetic field changes, kind of draging and/or pushing the rotor in either direction.

When the motor runs there will be a rotating magnetic field in the stator and the rotor follows this field. When the torque reaches a point where the rotor "lags" the rotating magnetic field too much it will "desynchronize", if the speed is high it will just plain stall. The good thing is that you can never destroy a step-motor by simply overloading it.

The rotor does not touch the stator at all, there's a VERY fins airgap between them. You should never open a step-motor in a dirty environment since, the magnets in the rotor are very strong and will "suck in" small metallic chips from your workbench which will end up in the fine airgap and either lock the motor up completely or make run "strange".

Depending on the type of magnetic material in the rotor it's also advised against removing the rotor from the stator as it can then loose some of its magnetism. Same reason why you have what's called a keeper-plate on "ordinary" magnets. With that said I've personally had several motors appart to drill holes thru the shaft and they have been working afterwards. I don't have anything to measure the actual torque but I couldn't "feel" any difference.

/Henrik.