The Harken 2631 57mm Carbo Air® Quadruple Block with Swivel is a high-performance sailing block engineered for sailors who demand reliable, low-friction line control without added weight. Part of Harken's trusted Carbo Air® series, this quad block delivers a powerful 8:1 or 10:1 mechanical advantage, making it an ideal choice for mainsheet systems on dinghies, catamarans, and keelboats.
Carbo Air® blocks are constructed with nylon resin sideplates densely packed with long-glass fibers, resulting in a compact block with an exceptional strength-to-weight ratio — 60% stronger and 30% lighter than classic block designs. The sheave runs on Delrin ball bearings for smooth, free rotation even under heavy loads. All components, including the ball bearings, sheave, and sideplates, are UV-stabilized with carbon black for long-lasting protection against harsh marine environments.
The integrated swivel attachment keeps lines from twisting under load, while the 3-Way U-Lock system allows the shackle to lock securely in front or side positions, or swivel freely as needed.
Key Specifications:
- Sheave Diameter: 57 mm (2-1/4 in)
- Block Length: 121 mm (4-3/4 in)
- Maximum Line Diameter: 10 mm (3/8 in)
- Maximum Working Load (MWL): 2,380 lb (1,080 kg)
- Breaking Strength: 5,000 lb (2,270 kg)
- Shackle Pin Diameter: 6 mm
- Weight: 12 oz (340 g)
- Attachment: Swivel with 3-Way U-Lock
Well-suited for main and jib sheet systems on centerboard and keelboats such as Lightnings, Dragons, Solings, and J/24s, as well as mainsheet systems on catamarans, the Harken 2631 offers the performance, durability, and versatility that competitive and recreational sailors rely on.
