If it's RAR (or PAR), there is usually a header (first) file with a suffix .rar or .par.
PARs are used for rebuilding partial file sets though, so if you don't have at least some of the uncompressed files to begin with, the PARs will probably do you no good. RAR is often used to compress and split up one large file, though it can also be used for sets of files. UnRarX will do both the RARs and PARs.