03.55 Heavy Duty Mast Block with 38mm Removable Plastic Sheave03. 55 Heavy Duty Mast Block with 38mm Removable Plastic Sheave These 316 stainless steel bodied turning blocks offer a range of stanchion mounting configurations. They are particularly useful for running furling headsail lines back to the cockpit. They are low maintenance and will continue to look good for years to come. The hinged action allows the nylon sheave to pull into line as rope leaves the furling drum. The rail mounted stanchion base (03