Ronstan Series 75 Single Core Sailing Block

The Ronstan Series 75 Single Core Sailing Block is a high-load single block for mainsheets, halyards, spinnaker sheets, and control lines on larger sailboats. Its 75mm format gives the rope a generous turning radius while keeping the assembly more compact than a traditional heavy utility block. A universal head provides three-axis articulation, allowing the block to follow a changing lead instead of forcing the load through a fixed angle. Ronstan positions the Core range for sailors who need strong hardware with lower friction and less bulk around the working end of the rig.

The sheave is made from UV-stabilized Acetal, while aluminum-alloy cheeks carry the structure around the bearing system. Grade 316 stainless steel is used at the head and primary load path for corrosion resistance in exposed deck installations. Ronstan's universal bearing arrangement is designed to remain efficient through both moving and static loads rather than feeling free only when lightly loaded. The combination works well in cruising systems that see long periods under tension as well as racing applications with frequent trimming.

• 75mm single-sheave Core configuration
• Universal head with full three-axis articulation
• UV-stabilized Acetal sheave
• Aluminum cheeks with Grade 316 stainless load hardware

The block is sized for line up to 14mm (9/16 in) and is rated for a 3,300 lb maximum working load with a 6,600 lb breaking load. Ronstan lists a weight of about 12.5 oz, keeping the assembly relatively light for the loads it can handle. Give the universal head room to articulate and verify that the line enters the sheave squarely through the full range of sail trim. For more high-load blocks and larger-boat rigging components, browse more Sailing Hardware.