The vajra and bell form part of the traditional ritual item set used by tantric practitioners. They are not to be used unless one has received higher tantric initiations or has the permission of one’s Guru to use them.
The vajra represents the male energy of compassion, Bodhicitta, while the bell represents the female energy of wisdom, realisation of emptiness. Used together, the vajra and bell remind us of the balance between male and female energies within ourselves. When both energies are invoked, we create the causes to attain the union between compassion and wisdom, which is Enlightenment itself.