M.T.U.

M.T.U is a hardmode crafting bench that is used to swap modifiers between items. It can be purchased from the goblin tinkerer for 75 gold if Plantera has been defeated in the world. When clicked on a menu pops up with two boxes and a swap button. If two items are put in the modifiers are swapped. The swapping costs the player the two weapons selling prices combined.

Trivia

 * M.T.U means Modifier Trading Unit.