40mm dynamic blocks are perfect for use on main, jib and spinnaker sheets on dinghies and keelboat control lines. Bearings – 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 Head – Featuring a 360-degree swivel head with a 4mm shackle. The shackle is load rated higher than the block, so although it might look small, it's plenty strong enough! Becket - This block has a specific becket (tying) moulding. The becket allows you to make a purchase system. Ideal for Cunningham, outhaul and vang controls. Fiddle - The fiddle sheave is a 20mm dynamic bearing sheave. This ensures that any purchase systems run as smoothly as possible.