Marklin 210888 - 5-Pole Armature - 8 teeth for SFCM & LFCM motors (60903 & 60904)
8 teeth rotor (armature) as used in the 60903 and 60904 Digital conversion set.
Your SFCM most likely needs this armature. Your Large Flat Commutator Motors use this or the 7 teeth armature 214118. Simply remove your old 3 pole armature, and count the teeth.