40mm Dynamic Single Ultra-Strap Block.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.Ultra-Strap Ð Our patented Ultra-Strap is used in our 20, 30 & 40mm Dynamic blocks. The Ultra-Strap is unique when compared to other designs because of its coining process. This process strengthens the strap, making it more reliable and hard-wearing as well as making it rope friendly. The Ultra-Strap block is a great choice for dinghy jib or mainsheet systems. Becket - The 40mm range features a large central hole, which can be used as a becket (tying-off point). Specific becket variations are also available.Please Note - The picture used is of the A20401SR, removable ultra-strap block. This version, the A20401S, does not have a removable strap and so is riveted through the centre.