C. F. Keil and Franz Delitzsch on Deuteronomy 24:6

Various Prohibitions. - Deu 24:6. “No man shall take in pledge the handmill and millstone, for he (who does this) is pawning life.” רחים, the handmill; רכב, lit., the runner, i.e., the upper millstone. Neither the whole mill nor the upper millstone was to be asked for as a pledge, by which the mill would be rendered useless, since the handmill was indispensable for preparing the daily food for the house; so that whoever took them away injured life itself, by withdrawing what was indispensable to the preservation of life. The mill is mentioned as one specimen of articles of this kind, like the clothing in Exo 22:25-26, which served the poor man as bed-clothes also. Breaches of this commandment are reproved in Amo 2:8; Job 22:6; Pro 20:16; Pro 22:27; Pro 27:13.