This Article Contains information directly from the Pikmin Games. This article is based off of an Enemy/Treasure/Area/Cave/Pikmin/Character from the Pikmin series of Games.
The Brute Knuckles is one of the treasures you will find in Pikmin 2. It is a toy punching glove that is found inside one of the four Mamutas in the fifth sublevel in the Frontier Cavern. Defeat all the Mamutas in the area so they won't harm you as you carry the treasure back to the Pod. Make sure the Caustic Dweevils are gone so they won't carry the treasure on their backs. After you cash in the Brute Knuckles, you will get the Rocket Fist upgrade.
Being in the Explorer's Friend Series, it is part of the Exploration Kit.