Irwin makes these couplers that you can buy. I just like making my own small tools whenever I feel I have the time.
The main reason I decided to show this tool I made, was to show how I glued it up.
When you absolutely don’t want any glue oozing out of a side of the joint, you can cut a small groove along the glue joint. This was easy to do on this project, with a bandsaw. This lets any excess glue flow into the groove, stopping it from oozing out the side.
This worked out perfect, keeping the inside of the coupler glue free.
After the coupler is glued up, you need to drill out the center of the slot with a 3/8” bit, to accommodate the pin on the bar of the clamp.