In Tibetan, these are called Dorje. They are a symbolic representation of a Thunderbolt and Diamond. In ancient times they were used as a larger sort of weapon like brass knuckles. The models on the right seen in the main display image represent bells obviously. A bell is said to be the opposite to a lightning bolt. The combination of the Bell and Thunderbolt are a symbol of the union of these forces. Represents firmness of spirit and spiritual power. These can be added to a set of Tibetan Prayer beads.