When two thunderbolts are crossed it is called a Viswa Vajra. It is the emblem of Amoghsiddhi. In Buddhist Tantra, the word generally designates Sunya or Void which cannot be cut, cannot be destroyed but which destroys all evils.

The Vajra is the quintessential symbol of Vajrayana Buddhism, which derives its name from the vajra itself. The Sanskrit term vajra means 'the hard or mighty one', and its Tibetan equivalent dorje means an indestructible hardness and brilliance like the diamond, which cannot be cut or broken. The vajra essentially symbolizes the impenetrable, immovable, immutable, indivisible, and indestructible state of enlightenment or Nirvana.