I came across this note and saved it for you and all other Olympia SMx users; I do not know who the author is: "Can I just say, having been in the typewriter trade since 1975, PLEASE take it from me that the Group 1 (or Group 1001) ribbon intended for Olympia, Adler, Facit and many other makes DOES NOT have eyelets !! The ribbon mechanism is designed to trip and reverse when the ribbon gets taut as one spool becomes full and the other totally empty. Someone may well have fitted an eyeletted ribbon to a Group 1 spool as a bodge to get over a sluggish or badly adjusted ribbon reverse mechanism - to give the reversing fork an extra 'nudge'. The factory did not intend the ribbon to be reversed this way." In my experience, eyelets will often slip through the reversing arms and then hang up on the vibrator. You don't have to buy eyeletless ribbons; you can just cut them off the ends of your current ribbon and reattach to the spools.

the diameter of the spool spindle is different in all groups, so from the measurement of the spindle, you should be able to tell what group it is.