How to combine .001 files into a disk image?

I have two folders that I downloaded, the first folder is named DVD 1 the second DVD 2. Both contain files of the .001 type. There is a list of this kind of file type ranging from .001 through like .075 or how ever many in each folder. I can assume that this was a disk image that has been split into two separate file folders. I have combined with 7zip all of the files in each folder (DVD 1 and DVD 2) by right click>7zip>Extract Here. As I said, I have done this with each folder. Now I have these two massive files that need to be combined to make an ISO image. How?