How do you make rar sequence files like part1.rar part2.rar and so on?

open WinRAR go to "Option" -> "Settings" -> "Compression" at the Volume size list click "Define volume sizes..." in "User defined sizes" put this:

Label Size, bytes
1. 15 MB 15,000,000
2. 50 MB 50,000,000
3. 100 MB 100,000,000
4. 200 MB 200,000,000