Ronstan Core Block, Series 100 - Double, Universal Head

SKU: RF104200

Sale price$617.00 Regular price$650.31


A balanced design approach incorporating functionality, performance and style makes the Series 100 Core Blocks™ the right choice for performance cruising or racing applications. A full contact bearing provides excellent performance across the full working load range with an integrated thrust bearing feature and the resilience to handle high dynamic or static loads. Glass Fibre reinforced nylon sheave, alloy cheeks and stainless fixings complete the durable package.

Dynamic and high static load performance

Core Blocks™ incorporate a full contact acetal bearing on a polished stainless steel race to maintain low friction performance under heavy loads. Ball bearings are configured to act as a thrust bearing between the sheave and checks, preventing the sheave from rubbing on the cheeks and causing friction when the line lead in and out of the block isn’t perfect; particularly important for foot blocks.

Universal head

The head assembly incorporates a brass bearing washer to provide smooth 360° rotation of the post and shackle. A set screw arrangement allows the head to be locked at 0° or 90°. Shackles are high quality forged grade 17-4PH stainless steel.

Aluminium alloy cheek plates

Block cheeks are manufactured from the highest quality aluminium alloy for maximum strength and hard anodised for durability and corrosion resistance. Material optimisation and the cut-away design minimises weight and allows easy fresh water rinsing of salt and debris from the bearings. The hollow hub can be used as a becket take-off or tie-up point.


  • High dynamic and static load capacity
  • High load bearing system
  • Ball bearings to counteract side thrust loads
  • Class leading performance and sleek, contemporary styling
  • Durable aluminium alloy cheek plates
  • Central hub hole can be used as a becket take-off or tie-up point
  • Also available in Series 45, 60 & 75


  • Ideal for mainsheet, spinnaker sheet, vang, halyard and backstay applications on boats to 16m (53ft).
  • General applications on larger yachts


  • Bearings: High compression strength, self-lubricating acetal
  • Head post: Grade 2205 stainless steel
  • Shackles: Grade 17-4PH stainless steel
  • Padeye: Grade 15-5PH stainless steel
  • Other fixtures: Grade 316 stainless steel

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