40mm Dynamic Cheek Block.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.Cheek - Designed to be mounted flat to a surface using two fixing screws. Featuring a domed head to reduce the chance of lines snagging around the block. The central fixing point has two small drainage holes to ensure water can escape through the middle of the block.