This iron knuckels are forged by elves that master coldcrafting and can bend natures reality to their will.

By doing so they have managed to shape a rare kind of thorny briar from the forest into the base of the knuckles and then provide it with the characteristics of iron. 

Once per target and per turn, (not round), when you hit a creature with an unnarmed attack while wearing this knuckels you can choose to inflict a bleeding effect on it.

If you choose to inflict the bleed, the creature must succeed on a DC 15 CON save or suffer 1d6 damage that can't be resisted by any resistances. 

Creatures without the ability to bleed or secreet their inner selves such as most undead are innmune to this effect.

Notes: Damage: Unarmed Attacks