What is the core meaning of the root שלב?

QUESTION: What is the core meaning of root שלב? While you’re at it, please define “משלבות” in Ex 26:17 and also define/describe “שלבים” in Kings I 7:28 (even better if you can link to an image of the latter). Speaking of ladders, commentaries relate it to שליבות סולם. Is that because: A) rungs are layered in horizontal/parallel fashion (and hence משלבות of the two ידות of the קרש means that they were parallel to each other and of identical dimensions)? or is it because: B) rungs of a ladder are tenons that are mortised into each side rail, but not that they are necessarily parallel? Or is it both? If just B is correct, then משלבות of קרש means that the two ידות pegs were mortised into קרש-like rungs into side rail of ladder? Or that the ידות emerged like rung tenons that were to be mortised into the sockets? And if that is the case, then אשה אל אחותה doesn’t relate to משלבות, but is a separate thing, that they were parallel to each other? Rashi (to Ex. 26:17) seems to describe B: ” משולבות: עשויות כמין שליבות סולם, מובדלות זו מזו ומשופין ראשיהם לכנס בתוך חלל האדן כשליבה, הנכנסת בנקב עמודי הסולם. Accordingly, אשה אל אחותה is something separate, but also modifying the שתי ידות, i.e. that they were מכוון parallel, in addition to be משלבות “rung-like.” Or does אשה אל אחותה modify משלבות, that the they were layered like rungs next to each other (but not that the purpose of each yad was to be mortised into socket)? Or does שלב imply both, layered and tenons? Which brings me back to my original question: what is the core meaning of שלב?

Rabbi Michoel Green