: The .001 suffix indicates this is the first "slice" of a split volume. For the archive to be opened or extracted, you must have all subsequent parts (e.g., .002 , .003 ) in the same folder.
: Unlike a standard .7z file, the .001 file contains the central directory or "header" information for the entire set. If this specific file is corrupted or missing, the other parts (even if they are perfectly intact) become virtually impossible to extract because the program won't know the file structure or where one file ends and the next begins. SS-Tas-011_v.7z.001
An interesting feature regarding this specific file format and naming convention is its : SS-Tas-011_v.7z.001