M-series facility

M-series facilities were a type of Forerunner installation. All Huragok under Covenant employ were from M-series facilities.

Trivia
Halo: Cryptum describes Huragok as serving aboard semi-automated maintenance stations in the moons of the outer worlds of San'Shyuum home system; as such, it is possible that these are M-series facilities, with "M" possibly standing for "maintenance."