These nine-pronged dorjes have a piece of metal inside which produces a sound when the dorje is shaken or rotated. They are modeled after those found in a monastery in Kham, Tibet.
The origin of the dorje can be traced back to the thunderbolt of the Indian god of rain and weather, Indra. As the symbol of Indra, the thunderbolt was a flat, double trident. It was brought to Tibet in the 8th century by Padma Sambhava, the Indian founder of Lamaism, and used, as legend has it, to subdue demons. The Buddhists altered its form, giving it at each end four-eight prongs curved around a straight prong. The prongs come out of twp eight-petaled lotus flowers, which meet in a rounded center section. This is the typical Tibetan dorje. The nine-prong style is less commonly used.
The dorje is considered masculine, symbolizing Method or Compassion and is usually used in connection with the bell, which is considered feminine and symbolizes Wisdom or the Void.
The literal meaning of the Sanskrit word vajra or Tibetan word dorje is diamond, or prince of stones. In other words, that which is indestructible and unchanging. According to the Tibetan Kanjur, when Gautama became a Buddha during his meditation under the Bodhi tree, the gods sang his praises: "Reverence be to thee...whose mind is profound. Thou hast found the highest degree of perfection. Thou art immovable, firm fixed, like Mt. Meru or the scepter in the hand of Indra. Thou art constant in thy vow or resolution." So the thunderbolt is emblematic of the adamantine consciousness of the Buddha, or enlightened mind.