'Hollow' in the Bible

You are to make the altar hollow, out of boards. Just as it was shown you on the mountain, so they must make it.

He put the poles into the rings on the sides of the altar, with which to carry it. He made the altar hollow, out of boards.

Who has measured out the waters in the hollow of his hand, or carefully measured the sky, or carefully weighed the soil of the earth, or weighed the mountains in a balance, or the hills on scales?

He made my mouth like a sharp sword, he hid me in the hollow of his hand; he made me like a sharpened arrow, he hid me in his quiver.

Each of the pillars was about 27 feet high, about 18 feet in circumference, three inches thick, and hollow.