The defining abilities of Stark's armor are the jets situated in the boots and the repulsors situated in the gauntlets. The repulsors originated as a hand attachment, but have since become the armor's most important standard armament. They have been referred to as being magnetic, a blast of charged particles, and as a force beam. In the 2008 film, the repulsors are a form of propulsion and (as hand units) steering and braking jets, though Stark later learned that they could also be used offensively. A later variation on this is the Pulse Bolts, bolts of concussive energy that actually gain energy the further they have to travel, up to a limit of roughly three football fields (about 329 meters).