The Thorium collection is a set of plate with strength, crit rating, and armor pen, making it of particular use to dps warriors and paladins with the first piece available at level 45, all but the leggings available by 51, and the leggings becoming usable at 55. The set remains useful, though less than optimal, through the end of vanilla. The lower level pieces of the set will probably be replaced before the higher level pieces are obtained, either from quest rewards, world drops, or other crafted items such as the Imperial Plate set. Note that the Imperial Plate set was removed from the game, which isn't much of a loss, as this can easily carry you through to the Fel Iron Plate collection, which is the next lvl of gear available if you like to make your own gear for lvling purposes.