“ Beit Shammai says it needs a lehi and a beam, and Beit Hillel says either a lehi or a beam. Rabbi Akiva says that they argued about both cases. Mishnah 3
The beam which was mentioned, it must be wide enough to hold an ariah, and an ariah is half a brick of three tefachim. It is okay for the beam to be a tefach wide so that it can hold the ariah sideways. Mishnah 4
It [the beam] must be wide enought to hold an ariah and strong enough to hold an ariah. Rabbi Yehuda says it [the beam] must be wide enough, but it doesn't have to be strong enough [to hold an ariah] . ”

“ A caravan that is camped in a valley and is surrounded by animal related objects can carry within [that perimeter] only if the fence is 10 tefachim high and the gaps aren't larger than the walls. Any gap that is 10 amot is permitted because it is like a door ”