From Pikipedia, the Pikmin wiki
The Adamantine Girdle (はがねのはらまき?, lit.: "Steel Haramaki") is a treasure found in the game Pikmin 2. It is just a shiny nut which can be found on the fifth sublevel of the Subterranean Complex. Volatile Dweevils will fall from the ceiling at every turn, so it's best to run through the level and set them all off before trying to move the treasure.
“There appears to be a link between the treasures we found in an underground structure. We found several machine parts that fit together. The parts may provide a clue as to the original function of the area.”
“None want to believe it: a world so brutal as to require a steel torso guard for self-defense. It is certainly unattractive, but which do you value more: fashion or personal safety?”
This treasure's name consists of "adamantine", meaning unbreakable, and "girdle", something resembling a belt or cord worn around the waist. Its sales pitch helps contextualize this name, marketing it as a "steel torso guard".
Internally, the treasure is simply called
Names in other languages