Dharmachakra Amulets (Dharma Wheel).

The "Wheel of Dharma" (also called "wheel of Law) is the symbol that represent the doctrine and teachings of the Buddha.
It is one of the oldest Buddhist symbol, that appeared
around the time of Buddhist Emperor Ashoka,
before even any human form representation of the Buddha.

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Dharmachakra amulets are not very common, they are worn as relics
and souvenirs carrying the blessings of some Venerables,
and also as help to meditation practice.