2005 Cavalier front wheel hub assembly

I just installed a front wheel hub assembly on my 2005 Cavalier. Part was made by Timken. The install went great, no problems, car drives fine with the new part. My question is, the part came with a new axle nut, and an o-ring seal and a circular metal piece with a rubber seal in the inner circular cutout. The instructions mention nothing about these additional parts except to use one or both if needed. The old hub had neither o-ring or metal piece with inner seal. I put the o-ring on the new part where it mates with the steering knuckle. I could not figure out where to put the metal piece. What do you think, should I be using these additional parts? I can post pictures if needed.