Knuckles that drive spikes into their target on impact to increase critical power.
VII Pile Banger is a high-ranked weapon for Barret, providing 90 Attack, 80 Atk%, Critical +3%, and three linked materia slots with no growth. It can only be found in Shinra Headquarters during the Raid on Midgar. If not obtained, it is forever lost.
Pilebunker is a common weapon in fiction, but not necessarily used by robots only. Pilebunkers are sometimes built into a gauntlets.