29 mm Zircon Double Block

Harken 29 mm Zircon Double Block

The Harken 29 mm Zircon Double Block represents the latest expansion of the Zircon series, extending the lineup from eight models to eighteen. These smaller 29 mm sheave diameter blocks make Zircon technology accessible for control lines where multi-part purchases are required, filling a gap for performance dinghy and small boat sailors who demand immediate, precise response from their running rigging.

At the core of Zircon performance are industrial ceramic ball bearings mounted inside caged races. The cages keep the bearings separated so they cannot bunch up, touch, or stop one another — resulting in a remarkably free-running block that loses very little energy to friction. A free-spinning Zircon block, given a strong spin while unrigged, will continue spinning for an extraordinarily long time. Zircon ceramic bearings are more than 700% stronger in compression than stainless steel bearings of the same size, meaning they stay smooth under load and resist deformation within recommended limits. Crucially, they require less energy to begin rolling, making them especially responsive when load on the line is slight.

This responsiveness becomes critically important in light air or when fine-tuning sail shape. Whether easing a 24:1 Cunningham rigged under the deck or letting a jib lead forward for extra power through chop, the Zircon double block reacts immediately to even the smallest input. The result is more precise sail shape control and measurable gains in boat speed.

Key Features

• Industrial ceramic ball bearings in caged races for ultra-low friction
• Ceramic bearings over 700% stronger in compression than stainless steel equivalents
• 29 mm sheave diameter ideal for multi-part control line purchases
• Double block configuration for demanding rigging applications
• Maximum working load: 160 kg (350 lb)
• Breaking load: 480 kg (1050 lb)
• Accepts lines up to 6 mm (1/4 in) diameter
• Lightweight at just 20.4 g (0.72 oz)
• Compact 43 mm (1 11/16 in) length
• Part of the expanded 18-model Zircon series