In terminal, cd to the directory that contains the volumes and run 7z command on the first file from the sequence:
cd ~/Downloads
7z x asdf.iso.0
7zip should notice that you have a multi-volume archive and unpack everything. If you want the directory structure flattened, use 7z e instead of 7z x.
GUI Solution
Right-click the first package of those you downloaded (eg file.zip.001).
Make sure the p7zip-full and p7zip-rar packages are both installed. It is particularly p7zip-rar that is needed to provide RAR extraction functionality.
You can install those packages in the Software Center, or you may prefer to install them in a Terminal (Ctrl+Alt+T) by running:
Best Answer
I don't know why would you like specifically 7-zip's binary to extract RAR, but here we go:
To unrar files with... unrar:
To extract rar files with 7-zip:
e
andx
mean extract obviously.