Harken Zircon Block, 29mm Triple - #2189The newest Zircon offerings are six models with 29 mm sheave diameters. These expand the Zircon offering from eight models to eighteen. Zircon is not an all purpose alternativeno block is. But these smaller sizes make Zircon appropriate for control lines where multi part purchases are required. Zircon reacts immediately. So, when the pressure gets light and you ease that 24: 1 Cunningham rigged under the deck or want to let the jib lead forward for