Series 20 blocks are the perfect choice for all types of dinghy control line applications. Their light weight and high load ratings make them ideal for use in powerful, efficient purchase systems for boom vangs, outhauls, cunninghams and traveller controls. Precision molded 3/4" acetal sheaves for up to 1/4" line Grade 316 stainless steel ball bearings and 304 stainless steel load straps and head fittings UV stabilized acetal cheeks