GEARWRENCH EXT 3/4DR 16 81413 ExtensionGEARWRENCH EXT 3 4DR 16 81413 Extension An Extension Bar is a tool accessory used to extend the reach of a socket wrench or ratchet, allowing access to fasteners that are located in deep, tight, or hard to reach areas. It consists of a long, sturdy metal shaft with a square drive at both ends, one end connects to the ratchet handle, and the other attaches to a socket.