How do these exhaust sleeve nuts work?

[WH23G3G]

I got two long exhaust sleeve nuts for the RH side HP manifold on my 73 400. They look weird. I don't remember how they came off since it was years ago. Does it screw onto the factory stud on the head? And why is the other end of the sleeve nut tapped out for a 1/4 screw? I don't think I have any on the LH side. It looks like there is just two on the rear of the RH side manifold.

[tan top]

tube nuts just screw then on as normal  , the LH side ones the  extra thread tapped in the top is for the hot air take  duct