Our best selling oarlock, the NRS Superston Oar Lock is madeproprietary manganese bronze Superston alloy gives you amazing strength and outstanding rebound memory. The 5/8" diameter, 3-1/2" long shaft is precision-turned and drilled for a split ring. The horn opening is 1-5/8" with a 2-3/8" inside diameter. Oarlocks include Split Ring keepers. Don't forget to order a spare.