Ronstan Series 55 Ball Bearing Quad Orbit Block™ with Becket
The Ronstan Series 55 Quad Orbit Block™ with Becket is engineered as the upper block in powerful mainsheet systems, delivering maximum load handling in an exceptionally lightweight and compact form.
Its quad sheave configuration distributes load efficiently, while the orbital bearing design minimises friction and unnecessary mass. The result is one of the highest working load-to-weight ratios in its class, making it ideal for performance-focused sailors.
Ronstan’s 2-stage bearing system ensures consistent low friction across both low and high load conditions, maintaining smooth trimming and reliable performance in all conditions.
Key Features
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Quad sheave configuration for high purchase systems
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Ultra lightweight Orbit Block™ design
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2-stage orbital bearing system for low friction under all loads
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Highest working load in its class
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Integrated becket for clean system anchoring
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Swivel shackle head for unrestricted rotation
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Grade 316 stainless steel head fitting
Key Specifications
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Sheave diameter: 55mm
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Maximum rope diameter: 10mm
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Breaking load: 1500kg
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Safe working load: 750kg
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Weight: 316g
Applications & System Integration
The RF55410 is designed as the upper block in compact, high-performance mainsheet systems, forming the primary load-bearing connection at the boom.
It works in combination with the RF56330B lower block and Orbit 40 cascade blocks to create efficient multi-purchase systems.
A typical 8:1 mainsheet system is configured as:
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Upper block: RF55410 – Series 55 Quad Orbit Block™ with Becket (this product)
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Lower block: RF56330B – Series 55 Triple Orbit Block™ with Becket
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Cascade block: RF48109 – Orbit 40 Single Block
For increased purchase, a 9:1 system can be achieved by upgrading the cascade stage:
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Upper block: RF55410
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Lower block: RF56330B
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Cascade block: RF48209 – Orbit 40 Double Block
In both configurations, the RF55410:
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Acts as the primary upper load-bearing block
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Ensures smooth load distribution across multiple sheaves
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Maintains compact, efficient system geometry
These systems are ideally suited to:
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Dinghies and catamarans up to around 5.5m (18ft)
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Sportsboats and small keelboats requiring efficient mainsheet control
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Performance applications where weight reduction and smooth trimming are critical
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