The next time you download a massive file split into *.part01.rar through *.part20.rar , you will know exactly what to do. Keep all the pieces together, fire up 7-Zip or WinRAR, click on the first piece, and hit extract.
Avoiding Extraction Issues with Multi-Part RAR Archives - Eweka how to extract multi volume rar files
: If you have part1 and part3 , but part2 is missing, the extraction will fail. The next time you download a massive file split into *