Buddhist Studies:

A bell can be eight, twelve, sixteen, eighteen or twenty-two finger-widths in height. Its base must be round, above which is a vase surmounted by the face of the goddess Prajnaparamita. Above these are a lotus, a moon disc and finally a vajra.

The hollow of the bell symbolizes the wisdom cognizing emptiness. The clapper represents the sound of emptiness. The eight lotus petals are the four mothers and four goddesses and the vase represents the vase containing the nectar of accomplishment.

Paired with the vajra the bell represents wisdom, and as wisdom and method are an undivided unity so the vajra and bell are never parted or employed separately.