Albert Barnes Commentary Judges 19:29

"And when he was come into his house, he took a knife, and laid hold on his concubine, and divided her, limb by limb, into twelve pieces, and sent her throughout all the borders of Israel." — Judges 19:29 (ASV)

A knife - Rather, “the” “knife”. The single household implement used, not like our knives at our meals, but for slaughtering and cutting up the animals into joints for eating (Genesis 22:6, Genesis 22:10; Proverbs 30:14).

Together with her bones ... - Rather, “into her bones,” or “bone by bone, into twelve pieces.” The “pieces” are synonymous with the “bones” . There is something truly terrible in the stern ferocity of grief and indignation which dictated this desperate effort to arouse his countrymen to avenge his wrong. Compare to 1 Samuel 11:7.