The pallet fork or pallet lever is an integral component of the lever escapement of a typical mechanical watch. Its purpose is to release the escape wheel one tooth at a time, at each swing of the balance wheel, and also give the balance wheel small pushes to keep it going.
The lever is shaped like a 'T', and is pivoted in the center; in operation it rocks back and forth. On the arms of the 'T' are angled surfaces called pallets which alternately engage the teeth of the escapement's escape wheel. The central shaft of the lever ends in a fork, which gives pushes to the balance wheel's impulse pin, which is set off center in a disk on the balance wheel's shaft. To reduce friction, the pallets are made of precisely shaped pieces of ruby jewel. The pallet which the teeth first contact is called the entry pallet, while the other one is called the exit pallet.
Under the fork there is a projecting guard pin which passes through a notch in a separate safety roller disk on the balance shaft. In normal operation it doesn't have a function. Its purpose is to make sure the fork is in the right position to receive the impulse pin if a jar to the watch prematurely 'unlocks' the lever from the escape wheel.
Mechanical alarm clocks and kitchen timers use a less accurate form of the lever in which vertical metal pins are substituted for the pallet jewels. This is called a Roskopf or pin-pallet escapement, and was previously used in cheap pin-lever watches.