Thorium Tube

A Thorium Tube is created and mostly used by engineers.

Source
The Thorium Tube is crafted by Engineers with a skill level of 275.

The recipe for this item is taught by:
 * (the Master Engineering Trainer in Gadgetzan, Tanaris)
 * any of the Grand Master Engineering Trainers in Outland

Engineering

 * Biznicks 247x128 Accurascope
 * Core Marksman Rifle
 * Dark Iron Rifle
 * Flawless Arcanite Rifle
 * Major Recombobulator
 * Masterwork Target Dummy
 * Adamantite Scope (as of patch 2.3 it doesn't require a thorium tube to craft)