Vajracakra
Vajrachakra (वज्रचक्र) refers to the “adamantine circle” positioned in the sahaja-puṭa or ‘innate layer’ of the Herukamaṇḍala: a large-scale and elaborate maṇḍala of Heruka, consisting of 986 deities, as found in the Ḍākārṇava chapter 15.—The Herukamaṇḍala consists of four layers (puṭa) consisting of concentric circles (cakra, totally one lotus at the center and 12 concentric circles, that is, 13 circles in total).
The vajra chakra contains 36 pairs of Ḍākinī and Vīra (hero), collectively called Leader Heruka (Nāyakaheruka):
Ḍākinī & Vajraḍāka,
Lāmā & Viśvaḍāka,
Khaṇḍarohā & Padmaḍāka,
Rūpiṇī & Ratnaḍāka,
Pracaṇḍā & Khaṇḍakapālin,
Caṇḍākṣī & Mahākaṅkāla,
Prabhāvatī & Kaṅkāla,
Mahānāsā & Vikaṭadaṃṣṭrin,
Vīramatī & Surāvairin,
Airāvatī & Aṅkurika,
Mahābhairavī & Vajrajaṭila,
Surābhakṣī & Vajrahūṃkāra,
Hayakarṇā & Mahābhairava,
Cakravarminī & Ākāśagarbha,
Mahābalā & Padmanarteśvara,
Yāminī & Mahābala,
Kāminī & Jñānaḍāka,
Saṃcālanī & Dhairya,
Trāsanī & Sthairya,
Caṇḍikā & Mokṣa,
Icchāsiddhi & Upāya,
Mahājvālā & Cittavajra.
They each have one face and four arms; they hold a skull bowl, a skull staff, a small drum, and a knife; they and this circle is dark-bluish black in color.