Prayer wheels are called Mani wheels by the Tibetans. A prayer wheel is a wheel on a spindle, and on the wheel are written or encapsulated prayers or mantras. According the Tibetan Buddhist belief, spinning such a wheel will have much the same effect as orally reciting them.
These prayer wheels may be small and carried by pilgrims, or larger and fixed to the gates of monasteries or around stupas and chortens. Each turn of the cylinder generates as much merit as the reading of the sutra or the formula enclosed therein.