The rotation of the escape wheel is controlled by the pallets. Another reason the escape wheel teeth are slanted backward is as a safety measure. At rest one of the escape wheel teeth will be locked against a pallet. The old escape wheel was replaced. The hinged pallets both pointed the same way, opposing the rotation of the escape wheel. Each swing of the pendulum a pallet releases a tooth of the escape wheel. As the escape wheel pushes the pallet, the hinge moves away from the escape wheel. For this period the escape wheel is "locked" and unable to turn. The Riefler escape wheel and pallets are of a special design. The fourth wheel also drives the "escape wheel" of the lever escapement. When the pendulum lifted one arm far enough its pallet would release the escape wheel. The escape wheel must have an odd number of teeth for the escapement to function. The escape wheel, except in unusual cases, has 15 teeth and is made of steel.