Harken Carbo Air blocks are made of tough reinforced composite in a size and style to fit any system: singles, doubles, triples, quads; ratchets and fiddles; soft and hard attach. These small, compact low-friction blocks have very high working loads for safe, easy trimming. They are perfect for main, jib and spinnaker sheets on dinghies and sportboats and control lines on boats of all sizes. Carbo Air blocks are lightweight, strong and reliable fiber-reinforced composite construction. Ball bearings, sheave, and sideplates are UV-stabilized.