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. Cheek - Designed to be mounted flat to a surface using the three fixing holes. Becket - This block has a specific becket (tying) moulding. The becket allows you to make a purchase system.