Open Body Turnbuckle Eye to Eye. These turnbuckles feature an eye or hoop at each end. Their simple structure make them ideal for many uses where a tensioning device is required. In Marine grade stainless they are perfect for coastal environments. Sizes sold are the smallest at M5, with an extension range of 5cm, M6, M8, M10, M12, M16 all the way up to M20 with an extension range of 14cm. Where M is the diameter of the screw.