Leads external halyards, topping lifts and control line aft from the mast base. White Delrin sheaves, for line halyards, contain UV inhibiting additives to protect the sheaves from damaging ultraviolet rays. Carefully designed black aluminum sheaves accommodate both line and wire, providing a smooth surface for line and full support for wire to prevent flattening. All these blocks have polished stainless steel mounting flanges Cheek material is either black anodized aluminum, or polished stainless steel Maximum wire diameter for aluminum sheaves: 3/16"