Spellthreads are tailor-crafted augments that grant caster-class bonuses to leg armor. Like other augments, applying a thread will overwrite another augment or enchant on the item. The Burning Crusade expansion is required for a tailor to craft spellthreads, but non-BC players can buy and use the threads on their equipment. Most tailors will only be able to craft 2 of the 4 available threads, because they must choose between Aldor or Scryers. Wrath of the Lich King expansion introduced several additional spellthread patterns.