Non-marking black rubber with 5/8" nylon inserts. Designed to support the bottom of your boat on the trailer; absorbs road shock. Heavy-duty steel sleeve and tapered design provide longer life, especially for heavy boats. Ideal as a replacement part or outfitting your trailer for the first time. Resists oil, fuel, and salt corrosion. Absorbs the shock of launching, loading, and hitching. Recommended max load - 400 lb. 10", 5/8" ID.