In Nepal we have this friend who has been doing wood working for many years. I have been carrying his products for quite a long time now. We have few of his creations in our online store. He made this mini prayer wheel/ key chain with craffted design of OM MANI PADME HUM around the unit. It measures 3 inches long and 1 inch diameter.
You can usually see a lot of people using prayer wheels in Tibet, Nepal and India while they go around the stupas, temples and monasteries. The script is the mantra of the Buddha of compassion, Avalokteshwara, (in Tibetan Chenrezig). It means HAIL TO THE JEWEL IN THE LOTUS. Mani means jewel and Padma means lotus. This is a very powerful mantra.