Harken soft-attach Fly blocks are designed to provide strength beyond mass, providing big power in a low-aero package. Designed specifically for high-tech line, these efficient blocks have an incredible working load for their small size. 18 mm blocks feature an integrated stainless-steel inner race and rivet, stainless steel ball bearings, and composite fiber-reinforced sideplates. Triples feature composite line guides that are integrated into the block head.