Concept2 oar collar for now obsolete sweep oars. See pictures for oar version. The company no longer manufactures the collars for this vintage.

This is an original drawing based on the collars that shipped with the oars. We've had one break at our rowing club, this is a stop-gap to get a few more years out of otherwise good novice blades.

Print is strait forward: PLA, Flat side down, 100% infill (these parts are under significant mechanical strain) and as fine as your printer will print. Be sure to print both halves.

You will need a hex nut at matching Phillips or socket head screw. M6 or 1/4-20 in your local standard.

Photos show an example of the original next to the reengineered version.