RAR is now the dominant method of compressing and splitting large files, but you will occasionally see files that look like this:
somefile.avi.000
somefile.avi.001
somefile.avi.002
somefile.avi.003
somefile.avi.004
These are MasterSplitter files, and once you download them you need to use MasterSplitter (shareware) to put them together. If there is no “.000” file, then the file was probably split with HJSplit (freeware). The first file that HJSplit makes uses the suffix “.001”.