Skitarii were generally divided into different types depending upon the role they were expected to play on the battlefield.
Balisteria - The Balisteria were the artillery units of the Skitarii. The artillery used by the Skitarii ranged from Thudd Guns to massive Ordinatus pieces. The term Balisteria included both the vehicle or artillery piece, as well as the Skitarii crews manning them.
Cataphractii - The Cataphractii were the Skitarii's armour units. The Skitarii made use of everything from small armoured personnel carriers like the Chimera and Rhino to heavy combat walkers and super heavy tanks such as a Baneblade.
Classiarii - The Skitarii forces of the Adeptus Mechanicus take a variety of forms. On warships and Explorator vessels operating within the Koronus Expanse and the Calixis Sector, specially-programmed Skitarii are a necessity, for they serve as the members of boarding parties, security personnel and bodyguards where other forms of Skitarii would be impractical. Within the Mechanicus territories of the Calixis Sector, these warriors are known as Classiarii, a term of obscure meaning within the ancient traditions of the Calixian Mechanicus, believed to mean "mariners." Nigh-impervious to vacuum, fitted with thick, implanted armour, and equipped with an array of implanted weaponry designed for void combat and combat in the cramped enclosures of a starship, a Classiarius trooper is literally built for ship-to-ship combat.
Herakli - The Herakli were Skitarii heavy fire support specialists. These massive, vat-grown cybernetic soldiers were as large as Space Marines and were capable of carrying heavy laser weapons and multi-barrelled Autocannons with ease. The Herakli wore heavy red robes and cowls that were covered in Mechanicus sigils and were protected by thick ceramite amour plating that covered their chests and shoulders.
Huscarls - The Huscarls were the personal bodyguards of Skitarii officers and commanders, hand-picked by these individuals and trained by them to perfection. The duty of the Huscarls was to protect their commander in the heat of battle and make sure that no debilitating harm came to him.
Hypaspists - Hypaspist Skitarii were the most basic augmented infantrymen of the Tech-Guard and were armed with cybernetically hard-linked Lasguns similar to those used by the soldiers of the Imperial Guard. Hypaspists were generally more powerful and skilled soldiers than standard Guardsmen as a result of the cybernetic enhancements that made them stronger and more accurate than normal humans and the psychosurgery they had undergone to suppress their emotional reactions and make them immune to panic or fear. However, this enhancement also made Hypaspists less independent and able to think for themselves in combat.
Praetorians - The Praetorians represented the most elite troops to be found amongst the Skitarii. They were super-enhanced humans augmented by a wide array of cybernetics and integrated heavy weapons. However, many old Imperial sources also suggest that Praetorians are instead an elite Skitarii type similar to Imperial Guard Storm Trooper units, but possessed of advanced bionic augmentations, putting them somewhere in combat effectiveness and elite status between Storm Troopers and Space Marines. Some Praetorians are in fact a form of Combat Servitors, rather than living, cybernetic humans. They move on tank treads and are armed with powerful heavy weaponry, such as Plasma Cannons. All of these different variations of the Praetorian Skitarii are completely plausible, and based on the preferences of the Mechanicus Magi who build them.
Tribunes - The Tribunes are the officers of a Skitarii unit. Though all Skitarii ultimately bow to the authority of the Adeptus Mechanicus' Magi and Archmagi, these are all command personne found at the grand strategic level. The Tribunes handle the day-to-day tactical and strategic command roles for the Skitarii.
Venatorii - The Venatorii were created in the wake of the War of Brass that devastated the Skitarii Legions of the Lathe Worlds, leaving entire Forge Worlds of the Calixis Sector with virtually no troops left. The reigning High Fabricator started a discreet rearmament drive throughout the Calixian Forge Worlds. The more military minded Tech-priests were moved into position to help replenish the fighting ranks of the Mechanicus within the sector. It took many years to bring this grand plan together, but once everything was in place, the High Fabricator of the Lathes found himself with a new force consisting of some of the best-trained and best-equipped troops in the Calixis Sector. Dubbed the Venatorii, the new hunters were a force that was to remain separate from the recovering Calixian Skitarii forces and act as the true elite troops of the Lathes. With their unique organisation and frightening red armour, the few outside of the Mechanicus who were aware of their existence soon began to call them the Crimson Guard.
Executors Fetial - The Executors Fetial are the diplomats and ambassadors of the Titan Legions, and are noted to have undergone much of the same combat conditioning as the Skitarii, save for the rampant muscle mass increase and inducement of an adrenal battle trance. It is unknown if the Executors are considered to be official members of the Tech-Guard.