Machined and balanced from billet 7075 Aluminum.... The same material sailboat masts are made from. The last coupler you'll ever buy!! Fits 1" prop shafts and 1" output shafts. Measures 4 7/8" long and 2 1/4" in diameter. Our coupler runs concentric with the prop shaft due to our unique balancing grooves, no more wobble!! Utilizes 6x 5/16" bolts for clamping and 2x set screws for safety. Standard 1/4" keyway. Coupler comes with all hardware described.