Item #879838

Ronstan 40 mm Series 40 Orbit Block - RF45151

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Ronstan 40 mm Series 40 Orbit Block - RF45151

Item # 879838


The Ronstan 40 mm Series 40 Orbit Cheek Block (RF45151) boasts the highest strength-to-weight ratio available. This is achieved through all-composite reinforced polymer materials and multiple attachment options. Their precision design provides the optimum number of ball bearings for minimum friction while weight reduction is achieved through the use of fiber-reinforced composites in the block head.


  • Lightweight
  • Highest working load in its class
  • Secure, versatile and secure attachment
  • Low profile and compact
  • Ultra low profile thru-sheave becket
  • Low friction 2-stage ball bearing system provides consistent performance over the full working load range


  • Mainsheet systems on dinghies, sport boats and small keelboats to 9 m (30 ft)
  • Spinnaker sheets on dinghies, sport boats and small keelboats to 9 m (30 ft)
  • Halyard, Vang and Backstay application on boast to 8m (26ft)
  • Control line applications on larger yachts


  • Safe working load: 715 lbs (325 kg)
  • Breaking load: 1540 lbs (700 kg)
  • Weight: 1.1 oz. (32 g)
  • Sheave diameter: 1-9/16" (40 mm)
  • Maximum line size: 5/16" (8 mm)
  • Materials:
    • Sheave: High compression strength carbon black Acetal
    • Ball Bearings: High compression strength Acetal
    • Stage 2 bearing - Carbon fiber reinforced, PTFE impregnated Nylon
    • Frame/Cheeks: Toughened, glass fiber reinforced Nylon


Kilogram for kilogram of working load, BB and RT Orbit Blocks™ are the world's lightest. To gain peak performance, Ronstan engineered out the heavy steel load straps, head post, shackle, full-length fasteners, and cleating accessories. Through extensive research and development, they replaced virtually all metal components with high-tech polymers and fiber equivalents. The unique orbital design allows the bearing to only be in the active areas of the floating sheave. This minimizes the mass of the inactive return race and hub. Weight and bulk are further reduced in the different block configurations. The ball bearing single and becket block has a through-sheave becket arrangement. The result? The lowest weight possible. Multi-sheave blocks have only single intermediate cheeks and an ultra-light and efficient head arrangement. This gives a 30% weight saving advantage over the nearest competitor. Other brands just link together their single blocks. This results in unnecessary double cheeks between each sheave, held together by a heavy steel channel across the top of the block.

Highest working load in its class

The orbital ball-bearing arrangement gives the largest possible bearing race diameter. This maximizes load performance. The proven Ronstan 2-stage bearing system features high compression grade acetal ball bearings and a secondary full-contact bearing. This gives minimum friction across the full working load range. The floating sheave and bearing system is supported by a fiber-reinforced load frame. The design was computer modeled to be stress optimized.

Part Numbers for Ronstan 40 mm Series 40 Orbit Block - RF45151

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