The Barton Marine 30mm sheave, Series 1 pulley blocks with its stainless steel frame for added strength is available in both plain and ball bearing options The blocks have a modern design with high strength and lightweight features, which allow for a multitude of uses on every size of craft. Available as Plain or Ball Bearing Blocks. Plain bearing blocks: Barton plain bearing blocks have a precision moulded acetal sheave running on a large diameter brass bearing, ensuring free running under the highest of loads. Ball bearing blocks: With our unique super-low friction ball race systems, featuring acetal sheaves and delrin ball bearings, running on a large diameter centre boss. This allows us to fit more load-bearing balls, which ensure extremely low friction performance, even under high loads.