Stoltz Ultimate Bow Stop 4" With End Bells #ULT4Fits 4" Wide Bracket. Complete set including mounting hardware.Made of polyurethane, to replace rubber and PVC rollers that need frequent replacement. Although they cost more initially, their long life makes them economical in the long run. Polyurethane is extremely cut and abrasion resistant. Won't split or crack, even in extreme cold.NONMARKING:Our rollers do not leave the black scuff marks that black rubber rollers do. No more hard work cleaning the bottom of your boat. We have seen catalogs advertise black rubber as "nonmarking", but that just is not true.