ASME VIII-1 Encapsulated Head Calculation

[PennyPacker777]

I am currently in the process of doing a calculation to determine the minimum thickness or operating pressure of an unstayed flat head or cover. Mabe I'm confused as to what the definition of a head is, but in FIG. UG-34 there doesnt' seem to be an illustration depicting a threaded head encapsulating the threaded body of a vessel (kind of like a cap or a lid). The closest image is figure Q, in FIG. UG-34, but in reverse. The head actually has internal threads and the body has external threads. Is there a way to asses this connection, or does this not apply? I assume that the thread shear will be the limiting design condition, but I'd like to show that with a comparison calculation. I've attached a horrible sketch so that you can see what I'm talking about.
Any input is appreciated