Marine 316 Grade Stainless Steel.High-temperature weather, stronger anti-rust, abrasion resistance. Dimension:Tube size 1-5/8”, Length: 2”, Shaft Diameter: 1/2 inch (12.8 mm) Adjustable Diameter fits oars from 1.34 inch -1.8 inch (34 mm-46 mm) The mounting plate rotates clockwise, which prevents the row lock from falling off, and the release line lock needs to rotate counterclockwise The Clamp-On Oarlock fastens securely to the oar with one adjustable bolt with no drilling required. Easy to install,suit for small boats,canoe,kayak,dinghy, lifeboat, water raft boat.etc. 1.Marine Grade 316 Stainless Steel 2.Tube size 1-5/8”, Length: 2”, Shaft Diameter: 1/2 inch /12.8 mm. 3.The Clamp-On Oarlock fastens securely to the oar with one adjustable bolt with no drilling required. 4.The mounting plate rotates clockwise, which prevents the row lock from falling off, and the release line lock needs to rotate counterclockwise