Basic unzip and unrar works, but multi-volume “part1.rar” doesn’t work

It says it supports extracting multi-volume “part1.rar” or “part01.rar”, etc archive files, but when I double click the set of far files starting with the first, an error dialog that says “unknown file format” pops up.

guluguy about Bandizip X - Zip, Rar, 7z Extractor/Unarchiver