The nut helmet is an invention made by Sandy that appears in the episode "Chimps Ahoy."
The nut helmet is a metallic helmet with two antennas on the sides and goggles on the front. It also has a peanut symbol on the front.
Role in episode
This helmet allows the user to communicate with nuts. SpongeBob can hear a nut saying, "It's dark in here." SpongeBob can then hear a peanut being made into a "nuticcino" after Sandy used her other invention, the nuticcino machine.
Technically, a peanut is not a nut. Therefore, it is not possible that the helmet can be used on peanuts. Either that, or it is not named correctly, and it is made specifically for peanuts, not nuts.