Harken 100mm Aluminum Stand-up Block - #3254Black Magic Air blocks are a top favorite of Big Boat performance racers and cruisers. These lightweight, free running, powerful performers are used for sail controls that see lots of action. Sideplates and sheaves Hard Lube anodized for maximum UV protection and a smooth surface. Center cage keeps Torlon roller bearings separated and parallel to reduce friction. Torlon is a registered trademark of Solvay Advanced Polymers L. L. C.