Got lucky

It is only necessary if you intend on retaining the factory style tapered roller bearings. If you convert to the newer style green bearing kit, you can toss it. Some say the old factory tapered roller bearings are stronger than the green type bearings....the old school in me tends to agree, but many more other types of axles have run the green type bearings for decades with great success....so I think the jury's still out on that. Probably not enough difference in strength to notice.