The NRS Superston Open Oarlocks are the finest whitewater open oarlock available! Made of Superston, a proprietary manganese, and the strongest bronze alloy of its kind. Superston's composition assures unmatched strength and remarkable corrosion resistance under severe conditions. The 5/8 in. diameter, 3-1/2 in. long shaft is precision-turned and drilled for a split ring. The horn opening is 1-5/8 in. with a 2-3/8 in. inside diameter. Oarlocks include Split Ring keepers. Oars with rope wraps or oar sleeves may sometimes fit snugly in oarlocks. Compare the measurements to those of your oar shaft to ensure a good fit with these oarlocks. Horn opening is 1 5/8 in.