Brass knuckles (variously referred to as knuckles, knucks, brass knucks, knucklebusters, knuckledusters, knuckle daggers, English punch, iron fist, paperweight, or a classic) are "fist-load weapons" used in hand-to-hand combat. Brass knuckles are pieces of metal shaped to fit around the knuckles. Despite their name, they are often made from other metals, plastics or carbon fibers.

Designed to preserve and concentrate a punch's force by directing it toward a harder and smaller contact area, they result in increased tissue disruption, including an increased likelihood of fracturing the intended target's bones on impact. The extended and rounded palm grip also spreads the counter-force across the attacker's palm, which would otherwise have been absorbed primarily by the attacker's fingers. This reduces the likelihood of damage to the attacker's fingers. It also allows its user to break glass windows without injuring their hands, thus are widely utilized in vehicle theft to break car windows.