Series 20 Single Block with Shackle Head


In stock online.
Model # 1787118 | Mfg # RF20100 | UPC # 9316800255504

Ball bearing blocks deliver high performance and sensitivity for static and dynamic loads.

A smooth and efficient block is critical to the conversation between sailor and boat—especially for hand-held control lines. Ronstan designed the Series 20 to give dinghy and small keelboat sailors the feedback to detect subtle wind changes and sail as efficiently as possible. These light-weight blocks feature a durable, UV stable acetal sheave that runs smoothly on a two stage system of low friction bearings. Acetal ball bearings handle moderate loads for high efficiency. As forces increase ball bearings can become distorted; shy of distortion a plain acetal bearing running on a stainless steel race shoulders the load keeping the ball bearings safe from damage while maintaining low friction. Fiber reinforced nylon cheeks provide rigidity and strength and are beefed up 316 stainless steel load straps. The included shackle features a pin with a low-profile head to prevent snagging on smaller lines. Get the subtle messages your boat sends you though the lines by using efficient and smooth Ronstan series 20 blocks.

This 20mm single with shackle head is versatile and can be used for a wide range of applications. Great for halyard tuners, Cunninghams, dinghy sheets and more. 

Key Features

  • Light weight blocks designed for moderate to high static and dynamic loads
  • Ideal for hand-held control lines
  • Unique two stage bearing system:
    • Acetal ball bearings deliver efficiency for moderate loads
    • Sliding acetal bearing on stainless steel race handles high loads and maintains low friction
  • Fiber reinforced nylon cheeks to add strength while reducing weight
  • UV stable acetal sheave is strong and light-weight
  • 316 stainless steel load straps add strength
  • Ideal for:
    • Dinghy sheets
    • Halyard tuning systems
    • Backstay systems on dinghies and smaller keelboats
    • Boom vangs (cascade systems)

Ronstan Selection Guide

Sheave DiameterLine CompatibilityShackle Pin Diameter
20mm1/4" (6mm)1/8"
30mm5/16" (8mm)5/32"
40mm3/8" (10mm)3/16"
50mm1/2" (12mm)3/16"


Series 20 Single Block with Shackle Head

Name Value
Ball Bearings Stainless Steel
Becket No Becket
Diameter 1/4 Inch or 6 mm
Direction Any
Integral Cleat No Integral Cleat
Mount Type Swivel Shackle
Ratchet Non Ratcheting
Safe Working Load 550 Pounds
Sheave Diameter 20 mm
Type Single
Weight 0.7 Ounce


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