Harken Carbo Air blocks are made of tough reinforced composite in a size and style to fit any system: singles, doubles, triples, quads & quints; ratchets and fiddles; soft and hard attach. They have very high working loads for safe, easy trimming and are lightweight, strong, reliable and affordable. The Carbo fiddle block line features high-load ball bearings with fitted races for low-friction operation. The 57mm fiddle features the Cam-Lock locking system. The switch allows the shackle to lock at 90-degree intervals or to swivel freely. Carbo Air blocks are a lightweight, strong and reliable fiber-reinforced composite construction. Ball bearings, sheave, and sideplates are UV-stabilized.