60mm Dynamic Single Block. Designed for use on Keelboats and Catamarans for a range of applications from jib sheet to mainsheet systems and everything in between. The single block features a swivel lock, located at the head of the block. Simply turn the locking screw to either lock the swivel in 90-degree orientations or unlock for complete free spinning. Bearings Ð Dynamic Blocks feature our patented bearing system which uses twin rows of stainless-steel ball bearings running on a stainless-steel rail. This provides a superior load-carrying ability and longevity when compared to other bearing systems which run on a plastic rail. Becket Ð A large central hole not only reduces the overall weight of the block but also offers a rope friendly attachment, perfect as a tie-off point when being used in a cascade system.