Perhaps I explained myself wrong. I can find no way to get the brass center post to turn when placed into the tub drain. Turning the chromed knurled knob, (which protrudes out when the pop-up is in the tub) only turns the chrome portion of the pop-up which then spins freely around the brass portion which has the threads (see photo above).
Even were there enough room, I don't want to hold the brass center post. I need to Turn the brass center post.
Similarly, spinning the knurled knob fast would just spin the chrome part fast. There must be some trick to get it to engage and turn the brass part. And if it did by chance catch by spinning fast, it would probably seat so well I would never be able to remove it again if necessary.