The void mage helm is a piece of Void Knight equipment. It can be bought from a Void Knight for 200 commendation points, although a player must have at least 42 Attack, Strength, Defence, Hitpoints, Ranged, and Magic, along with 22 Prayer to buy and wear one. It is worn in combination with the other pieces of Void Knight Armour (Void knight top, Void knight robe and Void knight gloves) to achieve the designated set effect. The Void knight mace is not required for the bonus.
The Void mage set gives a +45% to Magic accuracy. This provides less accuracy and defensive bonuses than Ahrim's robes, but can be easily switched with the other sets. If wearing Elite Void Knight robes, the set gives an additional 2.5% increase to magic damage.