Lewmar 72mm Synchro Block - Single [29927201BK]72mm Synchro Block Single Lewmar's Synchro Blocks are engineered for speed, efficiency, and superior handling. Using a combination of scientifically optimized block geometry, a Free Spin bearing, and a self aligning head to reduce friction and increase efficiency by up to 40%, over budget blocks on mainsheet systems. Each component is perfectly synchronized with the movement of the rope, providing you with an easier, smoother transfer of power from