40mm Dynamic Single Swivel Hook Block with Fiddle.New for 2023.Made from high-strength, lightweight glass-loaded nylon and featuring AllenÕs dynamic bearing technology for a high-performance block suitable for keelboats and dinghies.40mm dynamic blocks are perfect for use on main, jib and spinnaker sheets on dinghies and keelboat control lines.Bearings Ð Dynamic blocks feature our patented bearing system which uses twin rows of stainless-steel ball bearings running on a stainless-steel rail. The ball bearings are caged for further friction reduction. These features provide a superior load-carrying ability and longevity when compared to other bearing systems.Swivel Hook Head Ð Featuring a 360-degree swivelling hook for super easy attachment. Ideal for lightweight control systems where removal needs to be quick.Fiddle - The fiddle sheave is a 20mm dynamic bearing sheave. This ensures that any purchase systems run as smoothly as possible.