crown wheel

from The Century Dictionary.

• noun A wheel having cogs or teeth set at right angles with its plane, as, in certain watches, the wheel that is next the crown and drives the balance. It is also called a contrate wheel or face-wheel.

from the GNU version of the Collaborative International Dictionary of English.

• (Mach.) A wheel with cogs or teeth set at right angles to its plane; -- called also a contrate wheel or face wheel.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun In watchmaking, an object of circular shape with contrate teeth, which meshes with the winding pinion and with the ratchet-wheel on the barrel-arbor used to wind-up the watch, respectively, to set the time.