Filling material is staple set in foam plastic block with protective bumper. The 8" blocks have one threaded flo-thru handle hole. Handle sold separately. Although these high-quality brushes are recommended for use on all types of vehicles, some finishes may be more susceptible to scratching than others; always test in an inconspicuous area before use. ACID-RESISTANT, Green Flagged Nylon, 2.5 inch bristles.