Harken's 18 mm Fly Soft Attach Block Narrow is designed to provide maximum strength in a lightweight, low-drag package. Specifically created for high-tech line, these efficient blocks boast an impressive working load considering their compact size. They are an ideal choice for foiling dinghies, sportboats, and high-performance racing yachts, and can be used in vang cascades and backstay systems. The 18 mm blocks feature a durable stainless steel inner race and rivet, smooth stainless steel ball bearings, and sturdy composite fiber-reinforced side plates. The 2161 "tight cinching" model is perfect for applications where the block needs to be secured as close to the deck as possible. Each block comes with a length of Spectra® line with a polyester cover, which provides exceptional strength and durability. (Use the registered trademark symbol after the first mention of Spectra®.) Part No. 2161 has a sheave diameter of 18 mm.