'Jacking is a form of corporal punishment employed in the Iron Kingdoms for the most severe crimes, when mere execution will not suffice. The offender is manacled to a steamjack at each limb, and the jack is marshalled to parade back and forth until such a time as the judicial officials involved are satisfied.
Sometimes the offender is manacled backwards onto the 'jack, so that his joints bend opposite to those of the construct, and he is rent limb from limb as soon as the construct begins to move. Even if this is not the case, the combination of being battered against the metal chassis of the steamjack and being burned from the radiating heat of its furnace typically brings a brutal end to the criminal's life. Those few that do survive are in no condition to commit further crimes, or indeed do anything at all other than live out their few remaining days as a broken invalid.