MULTIFLEX Heavy duty Trailer Keel Roller Allows boat to roll smoothly on the trailer. Spins freely to reduce drag while launching your boat. Heavy Duty Rubber Black Black rubber with 5/8"" Soft inserts. Sizes : 8Inch,10Inch, 12Inch. Heavy duty steel sleeve and tapered design provide longer life. Non-marring, durable rubber protects your boat’s finish. Molded rubber over steel tube with nylon end inserts. Extremely tough, designed specifically for heavier boats.