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 mmMaximum line Ø (in)5/16 inSheave Ø (mm)40 mmSheave Ø (in)1 9/16 inLength (mm)60 mmLength (in)2 3/8 inWeight (g)44.7 gWeight (oz)1.58 ozMaximum working load (kg)230 kgMaximum working load (lb)500 lbBreaking load (kg)680 kgBreaking load (lb)1500 lb