Cog (Donkey Kong Country 3: Dixie Kong's Double Trouble!)
From the Super Mario Wiki
A Cog is an item that appears in Donkey Kong Country 3: Dixie Kong's Double Trouble! There are five Cogs in all, and each one is critical in raising the Knautilus.
Whenever Dixie and Kiddy Kong clear a level for the first time in Krematoa, they receive a Cog upon raising the level's Level Flag. While the Kongs have no real use for any of the Cogs, by taking them to Boomer, he inserts them into a strange machine in his bomb shelter. Although the Cogs apparently do nothing at first, once all five of them are inserted into Boomer's machine, they reawaken the dormant volcano within Krematoa, and, more importantly, trigger the Knautilus into rising from Krematoa's lake.
In the Game Boy Advance version of the game, the Cogs are silver instead of gold.