- the Heruka Class, which includes the Chakrasamvara Tantra and Hevajra Tantra;
- the Permanence Class; and
- the Vajrasattva Class, which includes the Kalachakra Tantra.
The Mother Tantras are also sometimes categorized in six classes.
- Ringu Tulku, The Ri-me Philosophy of Jamgön Kongtrul the Great (Boston & London: Shambhala Publications, 2006), pages 86-93.