Practice Lock

Practice Lock is an item usually made by Engineers that could be used to practice Lockpicking. This was a slow and potentially expensive way to increase your Lockpicking skill.

The Practice Lock can only be used once. After that, it is opened and completely worthless. Many players practiced with renewable lockboxes off the Merchant Coast near Ratchet,  Amani Catacombs in Ghostlands or  Alther's Mill in Redridge Mountains.

On September 2, 2007, Blizzard patched-in support for the auction house telling potential buyers whether practice locks have been opened or not. Previous to this, unscrupulous players could auction their used practice locks to be bought by unsuspecting players.

With patch 4.0.1, the rogue lockpicking skill was changed to scale with a rogue's level, and no longer requires levelling through picking locks.

Source
Practice lock is made by engineers with a skill of 100.

The schematic is learned from a trainer.