With the steel washers the skinny arrows may not make good contact. The adapter simply is a beveled ring that is the diameter of the shaft on one side and is the diameter of the broadhead on the oposite side to fully support the base of the broadhead head.

Yes you still use the steel washer as the adapters are aluminum and the blades would simply crush the aluminum.

If I were shooting the axis arrows i would use the adapter rings with my slick tricks. It just provides full contact with the steel washer to lock the broadhead in tight.