Attaches the outhaul to the sail clew using an easy to use captive locking shackle. This clew shackle and block will stop the clew hook or line releasing midway through a race. Having a block attached to the clew of the ILCA Sail also provides an additional turning point for the outhaul line. Having additonal purchase on your outhaul system allows you to trim your outhaul more accurately, and sail faster. The 16mm Harken air block is included and comes fully assembled ready to use.