The .001 file contains the header information that tells the software how to stitch the rest of the pieces back together.
When a file—such as a high-definition video, a large software installer, or a massive database—is too large to be shared easily, users "split" the archive into smaller pieces. Fourth.7z.001
Because split archives are often used to distribute large software or media collections on forums and peer-to-peer networks, they are a common vehicle for malware. If you find a file named Fourth.7z.001 on your computer and don't remember downloading it, it is best to scan it with antivirus software before attempting to join or extract the parts. Do you have the of this file, or a large software installer