The Harken 57mm Double Zircon Block is designed to immediately adjust sail shapes to new conditions. Its industrial ceramic ball bearings and caged races make it the most efficient small boat block available. This block is offered in 40- and 57-mm sheaves, with or without beckets, and has a maximum working load of 300 kg (660 lb) and maximum line diameter of 10 mm (3/8 in). Part No. 2197.