is that the filename (the characters/letters before the period ".") or the extension (the characters/letters after the period ".")?
i just typed that string of letters "tda-ssf8" into google, and it brought up some torrents with the filenames:
tda-ffs8.001
tda-ffs8.002
tda-ffs8.003
...
if this is the case, WinRAR will likely take care of it, as you have been told.
looks like you need WinRAR 3.50 beta 1 (or later, if there is a later version). then, start up WinRAR, click on OPTIONS > SETTINGS > click on the INTEGRATION tab, and enter "001" under "User defined archive extensions" so that WinRAR will associate with that file type. click OK (until you get back to the main WinRAR window).
then, go to the folder/directory with the files (tda-ffs8), and right-click on the first file (tda-ffs8.001) and click on "Extract Files..." (and there should be a maroon WinRAR-looking icon by that option when you right-click on the .001 file). tell it where you want to extract the file, and WinRAR will "unpack" it all, as it's supposed to be.
no need to "string/sew" together the files beforehand.
let us know if this sorts out the problem.