Diamond-coated needle files cut with diamond-grit abrasive to abrade hardened alloy steels and other materials that are too hard for typical steel needle files. They also file ceramic, glass, and other brittle materials that a steel file would break. The grit coats the faces of the file and allows cutting in all directions for a superior finish compared to toothed files. Needle files cut, smooth, and remove material more precisely than precision files. Their slim body reaches into tight spaces and provides very gradual, focused material removal for decorative, intricate work in locksmithing, jewelrymaking, model building, electronics, die making, and small-scale metalworking.