20mm Double Dynamic Composite Cheek Block.Our Dynamic range is generally the best choice for applications that require constant sheave movement. Cheek blocks are designed to be fixed to a flat surface. Ideal for leading lines along a deck, into a cleat or around corners. Held in place by two screws. One screw through the middle of the sheave and the other through the countersunk hole in the head of the block. 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.