This roller assembly supports your boat's keel for easy loading and safe transport on your trailer. It features a 4-inch, black rubber spool roller and a galvanized steel bracket that attaches to your trailer's tongue.Features Spool roller supports your boat's keel as it sits on the trailer Prevents the bow from making contact with your winch Eases loading and unloading of boat Helps to absorb road shock while boat is being trailered Bracket lets you bolt roller assembly onto the tongue or frame of your boat trailer Sturdy, 0.13 in. galvanized steel bracket resists corrosion Black rubber roller delivers long-lasting performance Roller length - 4 in. Shaft diameter - 0.7 in.