FC 390-521P 31" 18SR .030" Polypropylene Cylinder Sweep/Scrub Brush for Factory Cat 390 Riding Floor Scrubbers. An economical alternative to the soft Nylon brushes, the poly scrub brushes are great for general duty scrubbing tasks on almost all flooring surfaces. The small .030" diameter poly reaches into cracks and grout lines. These can be used on sealed and unsealed concrete, polished concrete, older painted and epoxy painted flooring, tile and most stone surfaces. Usually white, black or blue in color. 31"L x 9"OD. Fits Factory Cat 390-C cylindrical scrub brush riding scrubbers. Some units (390, Disc) require two 20" disc brushes instead of cylinder brushes (use two 20-421P, .028" Poly Disc Brush - 19" block diameter). Please check your unit before ordering. Two cylindrical brushes create a 36" wide scrubbing path. Two brushes required. Priced each. Replaces Factory Cat 390-521P