This TAM syllable is the Goddess Green Tara's heart emblem. Green Tara is a female Buddha in Vajrayana Buddhism. She is known as the "mother of liberation". She is the goddess who bring you success and achievement in your work.
In addition, carrying the TAM syllable keychain amulet can protect you from fear and ward off evil spirits and demons.
The dimension of this feng shui amulet itself is approx. 3 3/4"x 1" x 3/8". It is made of alloy and embedded crystals.