The Nigh Invulnerability Belt is constructed by Engineers who have specialized in Gnome Engineering, and have an Engineering skill of 350 or more. It can be used by any Engineer with the sufficient (350) skill. The Nigh Invulnerability Belt is a secret Gnome Engineering recipe, available from either of the gnomish engineering trainers (Tinkmaster Overspark in Ironforge, or Oglethorpe Obnoticus in Booty Bay).