The .001 file contains the header information that tells the software how to stitch the rest of the pieces back together.
Most email providers and cloud services have strict upload limits. Breaking a file down allows you to send it piece by piece. Fourth.7z.001
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. When a file—such as a high-definition video, a
Older file systems (like FAT32) cannot handle individual files larger than 4GB. Splitting a 10GB file into three parts solves this. a large software installer
.001 indicates that this is the first volume in a sequence. You will typically see accompanying files named Fourth.7z.002 , Fourth.7z.003 , and so on. Why Do We Split Files?