Ronstan Series 40 Double Swivel Ball Bearing Block

The Ronstan Series 40 Double Swivel Ball Bearing Block is a versatile two-sheave block for mainsheets, halyards, vangs, and spinnaker-control systems that are trimmed frequently. Its swivel shackle head rotates through a full circle, allowing the block to align with the tackle instead of forcing the rope across a fixed cheek angle. Two sheaves make it useful in multi-part purchases where compact size and smooth movement both matter. The ball-bearing design is especially helpful on controls that are adjusted repeatedly during a race or active day of sailing.

Acetal or Torlon ball bearings support the sheaves to reduce friction across the working range. Cheek cut-outs provide access for rinsing and bearing inspection, which is useful after hard sailing in salt or grit. UV-resistant structural materials and stainless load hardware are chosen for regular marine exposure rather than indoor or protected use. The bearing and swivel systems work together so the rope can move freely while the block follows changes in the direction of pull.

• Double-sheave ball-bearing configuration
• Full 360-degree swivel shackle head
• Cheek cut-outs simplify bearing maintenance
• Low-friction Acetal or Torlon bearing system

Set up the purchase so both rope runs stay fair and the swivel head has room to rotate without contacting nearby fittings. A clean lead reduces side load on the bearings and helps the line wear evenly through the sheaves. Inspect the shackle, bearing access points, and rope grooves during normal running-rigging maintenance. For more ball-bearing blocks and multi-part purchase hardware, browse more Sailing Hardware.