Ronstan Series 40 Triple Swivel Ball Bearing Block

The Ronstan Series 40 Triple Swivel Ball Bearing Block is made for mainsheet and control systems that need three low-friction sheaves in a compact moving block. A full-swivel shackle head lets the assembly follow the purchase as the boat and sail trim change, which helps keep the line centered. Three sheaves provide the capacity for higher mechanical advantage without spreading separate blocks across several attachment points. The format suits dinghies, one-design boats, and small sportboats where fast adjustment and low running friction are both important.

Acetal ball bearings support the sheaves and reduce the effort required during repeated trimming. Corrosion-resistant load hardware carries the primary loads, while cheek openings make the bearing area easier to rinse and inspect. The triple arrangement places more rope in the moving block, so maintaining free-running bearings has a noticeable effect on the feel of the complete tackle. Its swivel attachment also helps prevent one sheave from being loaded harder than the others when the purchase changes angle.

• Triple low-friction ball-bearing sheaves
• Full-swivel shackle head for alignment
• Cheek access for easier bearing maintenance
• Designed for frequently adjusted sail controls

Reeve the purchase so each rope segment runs cleanly and all three sheaves share the load. Check the shackle orientation and available clearance before tensioning the system, particularly on compact dinghy installations. Fresh-water rinsing and periodic inspection will help keep the bearing system moving freely through repeated seasons. For more triple blocks and performance sail-control hardware, browse more Sailing Hardware.