'Millstone' in the Bible

“No one shall take a handmill or an upper millstone [used to grind grain into bread] as security [for a debt], for he would be taking a [person’s] life in pledge.

But a certain woman threw an upper millstone [down] on Abimelech’s head and crushed his skull.

Who killed Abimelech the son of Jerubbesheth (Gideon)? Was it not a woman who threw an upper millstone on him from the wall so that he died at Thebez? Why did you go so near the wall?’ Then you shall say, ‘Your servant Uriah the Hittite is also dead.’”

“His heart is as hard as a stone,Indeed, as solid as a lower millstone.