Ronstan Series 40 All Purpose Block - Double Block - Full Swivel Head

The Ronstan Series 40 All Purpose Block – Double Block with Full Swivel Head is the marine workhorse you need for rigging, sail control, and load management on sailboats and powerboats alike. After years on the water, any experienced angler or boater knows that mechanical advantage systems make the difference between effortless deck work and back-breaking labor. This double block design delivers proven performance across both dynamic loads—like trimming sails in gusty conditions—and high static loads, making it equally at home on fishing vessels managing heavy haul-backs or cruising sailboats managing mainsheet tension.

At the heart of this block system is Ronstan's self-lubricating Acetal polymer sheave design paired with polished stainless steel races—a combination that eliminates the need for constant maintenance while resisting corrosion in saltwater environments. The full swivel head allows 360-degree rotation, preventing line twist and chafe that would otherwise compromise rigging integrity during extended use. At just 0.2 lbs per unit, the Series 40 maintains minimal weight aloft, a critical factor for sailboat performance and fuel efficiency on larger vessels. The compact 3 x 2 x 5-inch footprint integrates seamlessly into existing rigging systems without requiring extensive modifications.

Whether upgrading a cruising sailboat's mainsheet system, rigging a center console for tournament fishing, or retrofitting a commercial fishing vessel, the Series 40 double block works across rope diameters and load ranges that define real-world boating. The swivel head design proves especially valuable when used as part of a tackle system where line must change direction repeatedly—think halyards, sheet leads, and boom vangs. Marine professionals and serious recreational boaters specify Ronstan blocks for their reliability in demanding salt-air conditions where inferior polymer or corroded hardware fails predictably. This block is sold individually; calculate your complete system needs before purchase to ensure adequate mechanical advantage and safety margins for your specific application.