The Harken^® Bullet Block Double Upright is a low-friction block designed to be mounted and used to lead control lines aft on boats where up to 5/16" (8 mm) line is used. Compact and lightweight with a sheave diameter of 1-1/8" (29 mm), these blocks have a fast trim and release easily under both high and low loads. Delrin^® ball bearings and sheaves give the ultimate low load performance, yet they are capable of working loads of up to 400 pounds (181 kg). The cheeks are also crafted from Delrin, which is UV-stabilized with a carbon-black additive for maximum protection, with marine grade stainless steel mounting brackets. The Bullet Block Double Upright is ideal to be used as a main or jib sheet block on dinghies, as well as perfect for various control line applications such as travelers, cunninghams, boom vangs and more on offshore boats.