scape-wheel

from The Century Dictionary.

• noun The wheel which actuates the pendulum of a clock.

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

• noun (Horol.) The wheel in an escapement (as of a clock or a watch) into the teeth of which the pallets play.

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

• noun The wheel in an escapement (as of a clock or a watch) into whose teeth the pallets play.