The Harken 40 mm Zircon Block, part number 2190, has a maximum working load of 115 kg (250 lb). It can handle a maximum line diameter of 8 mm (5/16 in) and has a sheave diameter of 40 mm (1 9/16 in). This block is designed for efficient use on small boats, with the help of industrial ceramic ball bearings and caged races that keep the bearings separated for optimal performance. Available in 40- and 57-mm sheaves, in both single and double blocks with or without beckets, Zircon blocks are the top choice for sailors looking to easily adjust sail shapes to changing conditions.