Thank You. So what I must have bought thinking it was an Adapter ring, was really just a Retaining ring. The boat tail is OK with the correct threads. I was told by the seller that it was the Adapter Ring for the Gen 2 Boat Tail.
While I have you here, I was wondering if there would be any benefit or not from sharing the load by using the top of the motor to push on a bulkhead that is epoxied into place, either by using the end of the casing to push, or by using a threaded rod screwed into the FC, thus taking some of the load off the Boat Tail/thrust ring.