Harken 57mm Aluminum Low Load Black Magic Block with Swivel

57mm Aluminum Low Load Black Magic Block with Swivel

Black Magic Air blocks are a top favorite of Big Boat performance racers and cruisers. These lightweight, free-running, powerful performers are used for sail controls that see lots of action: mainsheet, runner, halyard, and spinnaker systems. A center cage keeps Torlon roller bearings separated and parallel to reduce friction. Shackle blocks lock in two directions or swivel to keep the line from twisting. Low-load blocks have red isolators. They use Torlon rollers and 316 stainless steel shackles. Standard blocks have 17-4 PH stainless head posts. Torlon is a registered trademark of Solvay Advanced Polymers L.L.C.

Specifications:

• Sheave: 57mm/2-1/4in
• Length: 119mm/4-11/16in
• Weight: 154g/5.44oz
• Shackle Pin: 6mm/1/4in
• Maximum Line: 12mm / 7/16in
• Maximum Working Load: 7/16kg / 1655lbs
• Breaking Load: 1500kg / 3300lb

The Harken 57mm Aluminum Low Load Black Magic Block with Swivel is a high-performance sailing hardware designed for demanding sail control applications on large boats. Built with lightweight aluminum and top-quality Torlon roller bearings, this block ensures smooth, free-running operation even under frequent use. Its robust construction makes it ideal for applications such as mainsheets, runners, halyards, and spinnaker systems where reliable performance is critical.

The center cage design keeps the Torlon bearings aligned to minimize friction, while the shackle blocks can lock in two directions or swivel freely to prevent line twisting during maneuvers. The inclusion of red isolators distinguishes the low-load version, providing precise control for lines up to 7/16 inch in diameter. Crafted with durable 17-4 PH stainless steel head posts and stainless steel shackles, this block offers excellent corrosion resistance and longevity in harsh marine environments.

Measuring 2-1/4 inches in sheave diameter and approximately 4-11/16 inches in length, the Harken Black Magic Block weighs just over 5 ounces, making it suitable for high-performance racing and cruising vessels. It supports a maximum line diameter of 7/16 inch and a working load limit of over 1,600 pounds, with a breaking load capacity of 3,300 pounds. Designed to meet the rigorous demands of sailing professionals, this block combines durability, smooth operation, and ease of installation, making it an essential component for serious sailors seeking reliable line control hardware.

Features:

• Sheave Diameter: 57mm (2-1/4 inches) for efficient line handling

• Lightweight Aluminum Construction reduces overall vessel weight

• Torlon Roller Bearings ensure low friction and smooth operation

• Center Cage design maintains bearing alignment for consistent performance

• Swivel and Locking Shackle options provide versatile line control

• Red Isolators indicate low load capability for precise control

• Durable 17-4 PH stainless steel head posts and shackles resist corrosion

• Supports line diameters up to 7/16 inches for versatile use

• High maximum working load of 1655 pounds for demanding applications

• Robust breaking load capacity of 3300 pounds for safety and reliability