Harken 2631 57mm Carbo Air Quadruple Block with Swivel

The Harken 2631 57mm Carbo Air® Quadruple Block is a high-performance sailing block engineered for demanding sheet and purchase system applications. Part of Harken's trusted Carbo Air® line, this quad block delivers an exceptional strength-to-weight ratio in a compact, low-profile package—making it a go-to choice for racers and cruisers alike.

Carbo Air® Construction:

• Sideplate material: Glass-fiber reinforced nylon resin, densely packed with long-glass fibers for maximum rigidity and durability
• 60% stronger and 30% lighter than traditional Classic blocks
• Ball bearings, sheave, and sideplates are UV-stabilized with carbon black for long-term sun and weather resistance
• Delrin® ball bearings enable free-spinning sheave rotation even under heavy load

Key Specifications:

• Sheave diameter: 57 mm (2-1/4 in)
• Overall length: 121 mm (4-3/4 in)
• Maximum line diameter: 10 mm (3/8 in)
• Safe working load (SWL): 2,380 lb (1,080 kg)
• Breaking strength: 5,000 lb (2,270 kg)
• Shackle pin diameter: 6 mm
• Weight: 12 oz (340 g)

Swivel & Locking System:

• Features a 3-Way U-Lock system allowing the shackle to lock in front or side positions, or swivel freely to prevent line twist
• Swivel head keeps lines running fair across varying lead angles

The Harken 2631 is ideal for mainsheet systems, jib sheets, and multi-purchase purchase systems on centerboard dinghies, keelboats, and catamarans. It is particularly well-suited for building a 10:1 mainsheet purchase system on dinghy catamarans. Compatible with main and jib sheet applications on boats such as Lightnings, Dragons, Solings, and J/24s.