Mills in Fausset's Bible Dictionary

In the East two "circular stones" (reechahim), 2 ft. diameter, the lower fixed, and with the upper surface slightly convex, fitting into the upper stone's concavity. This stone has a hole through which the grain passes, above a pivot rising from the lower stone. About the pivot the "upper stone" (recheb, "the rider") is turned by a handle. Being moveable it could be thrown as a missile (Judges 9:53 Gesenius translated "a cut piece of millstone," not a fragment, but the whole with its carefully cut surface; Revelation 18:21). Two women (Matthew 24:41) facing one another, seated on the ground, both turned it round by the handle, the one supplying the grain through the hole. It was hard servile labor (Exodus 11:5; Judges 16:21; Isaiah 47:1-2; Lamentations 5:18). The mill stones were so essential for preparing food that they were forbidden to be taken in pledge (Deuteronomy 24:6). The cessation of the sound of grinding was a sign of desolation (Jeremiah 25:10; Revelation 18:22; Ecclesiastes 12:3-4, "the grinders cease because they are few ... the sound of the grinding is low".) Larger millstones were turned by asses; Matthew 18:6 "a donkey millstone" (Greek).