'Millstone' in the Bible

"A person shall not take a pair of millstones or an upper millstone, for {he is taking necessities of life as a pledge}.

But a certain woman threw an upper millstone on Abimelech's head and cracked open his skull.

Who killed Abimelech the son of Jerub-bosheth, if not a woman who threw an upper millstone on him from [atop] the wall and he died at Thebez? Why did you go near the wall?' Then you shall say, 'Your servant Uriah the Hittite also died.'"

Its heart is cast as stone; yes, it is cast as [the] lower millstone.