Harken Carbo Air blocks are made of tough reinforced composite in a size and style to fit any system. The Carbo Ratchamatic® is a load-sensing ratchet block that rolls freely in both directions under low loads and automatically engages the ratchet as loads increase. Shifting between ratchet and light-air modes is seamless. Unloaded main and jib sheets run out freely during mark roundings and asymmetrical spinnakers free instantly during jibes. Ratchet engagement may be adjusted to a higher or lower load according to strength and sailing style. The Ratchamatic cheek block mounts on either port or starboard. The holding power of the 57mm block is as high as 10:1. Carbo Air blocks are a lightweight, strong and reliable fiber-reinforced composite construction. Ball bearings, sheave, and sideplates are UV-stabilized.