Knuckles that drive spikes into their target on impact to increase critical power.
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 is found in Shinra Headquarters' shop during the Raid on Midgar. If not obtained then, 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.