FC 390-521S 31" 18 Single Row .050"/80 Grit Heavy Abrasive Cylinder Sweep/Scrub Brush for Factory Cat 390 Riding Floor Scrubbers. An aggressive abrasive cylindrical scrubbing brush for heavy duty scrubbing or stripping jobs. Long lasting .050" Tynex-A Nylon filament impregnated with 80 grit silicon carbide granules. Equivalent to Tough Grit. Usually black 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 20-421SS Super Grit equivalent, or two 20-421S Tough Grit equivalent - 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 390-521S