Ronstan Nylatron Sheave Box - Single Upright Lead Block [RF453]Nylatron Sheave Box Single Upright Lead Block Lead blocks are a low profile solution for leading halyards or other rig sail controls back to cleats or jammers. When mounted in an inverted position, are frequently used as upright leads. Features: The external tabs can be formed to fit the spar profile before fastening Applications: Typically used in dinghy spars for control lines such as outhauls Materials: Nylatron sheave Grade 316 stainless steel