Harken 57mm Black Magic Low Load Block Swivel

The Harken 57mm Black Magic Low Load Block Swivel gives lightweight, free-running line control for frequently adjusted big-boat sail systems. Black Magic Air blocks are used in mainsheet, runner, halyard, and spinnaker applications where high loads and repeated trimming demand efficient bearing performance and robust construction.

A center cage keeps Torlon roller bearings separated and parallel to reduce friction as the sheave rotates. The swivel shackle arrangement can be configured according to the supported attachment orientation, allowing the block to align with the line path while maintaining a compact high-performance rigging package.

Confirm maximum line diameter, published working and breaking loads, shackle orientation, lead angle, and attachment-point capacity before installation. Size every part of the system for the highest anticipated sailing load and never exceed Harken ratings. Inspect bearings, sheave, shackle, sideplates, line, and mounting points regularly for wear or damage.

• Roller-bearing construction supports frequently adjusted big-boat sail systems.
• The center cage separates Torlon rollers for efficient sheave movement.
• The design suits compatible mainsheet, runner, halyard, and spinnaker systems.
• The swivel configuration supports appropriate rigging orientation.

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