PURPOSE: To prevent decreases in the abrasive force and breaking resistance of the polyamide-filament bristles of a brush roll used for polishing steel plates by imparting good acid resistance to the bristles, and keeping the stiffness of the bristles while water is sprayed.

CONSTITUTION: A bristle 1 comprises either polyamide filaments 1a covered at their surface with a film of a halogenated polymeric compound with abrasive grains mixed therein, or a bundle of polyamide filaments with or without abrasive grains mixed therein, covered with a cover 11 or 11' formed by the spiral winding of fine synthetic-fiber filaments 1b or by a braided structure, with the surface of the cover covered with a film of the halogenated polymeric compound or with the cover 11 impregnated with the compound.