Matthew Poole and continuators on 1 Kings 7:31

31 And the mouth of it within the chapiter and above was a cubit : but the mouth thereof was round after the work of the base, a cubit and an half : and also upon the mouth of it were gravings with their borders, four-square, not round .

So he calls that part in the top of the Base which was left hollow, that the Foot of the Laver might be let into it, and fastned in it.

i. e. Within the little Base, which he calls the chapiter, because it rose up from, and stood above the great Base, as the Head doth above the rest of the Body.

Above the Chapiter; for the Mouth went up, and grew wider like a Funnel.

Either in breadth: or rather, in height, v. 35. whereof half a Cubit was above the Chapiter or little Base, as is said ver. 35. and the other half is here implied to be within it, and below it.

To wit, in compass.

So the innermost part, called the Mouth, was round, but the outward part was square, as when a Circle is made within a Quadrangle.