Black 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: mainsheet, runner, halyard, and spinnaker systems. 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.