Deuteronomy 24:6 No man shall take the nether or the upper millstone to pledge: for he taketh [a man's] life to pledge.
Job 41:24 His heart is as firm as a stone; yea, as hard as a piece of the nether [millstone].
Isaiah 47:2 Take the millstones, and grind meal: uncover thy locks, make bare the leg, uncover the thigh, pass over the rivers.