I don't usually get to respond early in the game here. Others answer the questions, and i lurk. By knob you must mean the knurled ring, at the end of the closer, with a setscrew just foreward? I apologize if this is too basic.
The spindle adapter has a key, and the slot in the collet locates there. Otherwise the collet can spin and not get tight.
The closer has a key to mate it with the back end of the spindle. Without that in place, the tube can loosen from the collet.
Collets have a range, and your stock may not be large enough to fill the collet.
I have a closer on my 10K cabinet model. It uses a pin, not a key, in the end of the spindle, to locate the unit, which never stays tight,
Again, I apologize if this is obvious to you.