New Security Bit.
Also known as Linehead and/or Gamebit.
These are repair tools used to remove the security screws from video game cartridges such as Genesis, Nintendo 64, Turbo-Grafx, Gamecube and PC-Engine consoles and others requiring this size bit.

Why would you want to take apart a Nintendo 64 game cartridge, or any other cart?
Because the Gamesave battery in the cartridge has more than likely reached the end of it's shelf life. The batteries were manufactured to be viable for ten years + or -.

Although the battery is not essential to play the game the battery is essential to save the progress in any game session. With an outdated battery you will have to start each session as if starting for the first time.

Sold separately is a 4.5 mm Gamebit.
Gamesave Batteries for Super Nintendo cartridges ( CR 2032 Lithium ) are available, although not yet listed.