The Ronstan RF104100 Series 100 Core Single Block is a premium, heavy-duty sailing pulley engineered for high-load applications on cruising and racing yachts. Featuring a 100mm glass fibre reinforced acetal sheave, it delivers smooth, efficient line handling even under extreme loads.

Designed with Ronstan’s advanced two-stage bearing system, this block combines a full-contact bearing for high loads with ball bearings that act as thrust bearings—ensuring low friction performance across both dynamic and static conditions.

Constructed using hard-anodised aluminium alloy cheeks and stainless steel fittings, the RF104100 offers exceptional strength, durability, and corrosion resistance—ideal for New Zealand’s harsh marine environment.

Its universal head with full 3-axis articulation allows the block to align perfectly under load and can be locked at 0° or 90° for optimal rigging setups.

Suitable for boats up to approximately 16m (53ft), this block is widely used in mainsheet, halyard, vang, and spinnaker sheet systems, where reliability and performance are critical.

Key Features

• 100mm sheave for high-load sailing applications
• Two-stage bearing system for low friction under all loads
• Universal head with 3-axis articulation for optimal alignment
• Head can be locked at 0° or 90° for controlled positioning
• Aluminium alloy cheeks for strength and weight reduction
• Ball bearings reduce side-load friction and improve efficiency
• Suitable for high-performance cruising and racing systems

Specifications

• Sheave Diameter: 100mm
• Max Rope Diameter: 18mm
• Maximum Working Load: 3250kg
• Breaking Load: 7500kg
• Weight: approx. 900g
• Pin Diameter: 10mm
• Construction: Acetal sheave, alloy cheeks, stainless fittings
• Head Type: Universal swivel head

Why Choose the Ronstan RF104100? 

For New Zealand sailors, the RF104100 delivers exceptional strength, efficiency, and reliability under heavy loads. Whether you’re cruising offshore or racing competitively, this block provides smooth operation and long-term durability in demanding conditions.

Its advanced bearing system and high load capacity make it ideal for critical sail handling systems, ensuring confidence and performance in NZ coastal and offshore environments.