Zircon blocks help trimmers match sail shapes to new conditions immediately. At the core of the Zircon performance are industrial ceramic ball bearings mounted inside caged races. The cages keep these bearings separated so they dont bunch, touch, and stop each other. The result is the most efficient small boat block Harken has ever made. Zircon blocks are available in 40- and 57-mm sheaves in single and double blocks, with or without beckets. Maximum line Ø (mm)8 mm Maximum line Ø (in)5/16 in Sheave Ø (mm)40 mm Sheave Ø (in)1 9/16 in Length (mm)60 mm Length (in)2 3/8 in Weight (g)22.9 g Weight (oz)0.81 oz Maximum working load (kg)115 kg Maximum working load (lb)250 lb Breaking load (kg)340 kg Breaking load (lb)750 lb