Prayer wheels are filled with mantras traditionally printed on strips of paper and tightly rolled around the core.  These days mantras are reproduced onto microfilm; the more mantras, the more powerful.  Prayer wheels can be small enough to be held in the hand, table-based or can be very large containing billions of mantras; prayers wheels can be bought in Tara Institute's Bookshop.

“One of the benefits of the prayer wheel is that it embodies all the actions of the Buddhas and Bodhisattvas of the 10 directions.  To benefit sentient beings, the Buddhas and Bodhisattvas manifest in the prayer wheel to purify all our negative karmas and obscurations, and to cause us to actualize the realizations of the path to enlightenment.”

Lama Zopa Rinpoche