Im assuming its from a downloaded game or something? Look for a .rar one with them, RAR split archives are split like that. Ex. File.r0, file.R00, file.rar
R00 and 001 is from old rar archive packaging if you download some of the old xbox games they might use this type of filename and winrar might not detect it as a file it can open, if so and you want to open it in winrar you can open winrar and select File, Open Archive,and select All Files in the dropdown box then open the *.R00 or *.001 file.