Barton Marine 58mm Diameter Ball Bearing Rope Sheave. Used throughout the complete Barton block range. Molded from UV-resistant acetal resin the Barton sheave is made to survive the harsh marine environment. The unique super-low friction ball race system features Delrin balls running on a large diameter center boss which ensures an extremely low friction performance. Package Contents: Barton Marine Diameter Ball Bearing Rope Sheave Barton Marine 64913: 58mm Diameter Ball Bearing Rope Sheave