The purpose of this washer is to hold the felt grease seal against the bearing so the grease doesn't escape from the bearing. If you are using sealed bearings this item is redundant. There is a small sleeve which fits over the shaft against the commutator, then this dished washer with the raised centre towards the bearing, the felt seal next, then the bearing. On the outside of the bearing there is another felt, a washer then a screw in the end of the armature shaft. However, if you are using sealed bearings you only need the sleeve and the bearing. It could be argued you don't need the sleeve either, as long as the bearing doesn't slide down the shaft when you're fitting it in its housing.