The brass knuckles are golden colored and have four holes on them to put your fingers in. On the knuckles enochian sigils are carved on them and they glow when activated.
In Keep Calm and Carry On, Ms. Watt attacks Dean Winchester and Castiel after they attempt to rescue Sam Winchester. She arms herself with a pair of brass knuckles with Enochian sigils carved on them. They proved effective as Ms. Watt was able to overpower Castiel and beat Castiel as well as Dean. She was later killed by Mary Winchester while she was distracted. Before disposing of her body Dean took her brass knuckles.
In Mamma Mia, Lady Toni Bevell beats and tortures Dean with an identical pair of Enochian brass knuckles but he doesn't break.
In Twigs & Twine & Tasha Banes, Arthur Ketch tells Mary that they only work on angels and will have no effect on him as he's not an angel. Mary promptly kicks him the crotch then punches him in the face with the brass knuckles, telling Arthur that "brass knuckles are brass knuckles."
In All Along the Watchtower, Mary Winchester dons Enochian Brass Knuckles for use against Lucifer. Wielding the knuckles, Mary is able to hurt Lucifer and knock him through a rift into an alternate reality, trapping him, but not before Lucifer pulls her through with him.