I wanted to design something to hold a pole right near my picnic table and found falconphysics' V-Groove Table Clamp to be the closed to what I had in mind. Remixed it a bit to suit my need:

• Chopped off the top part.
• Change size of the opening to clamp onto the table. Now suitable for table thickness of 33mm or less.
• Cut the screws so they can easily be printed flat which inspire much more confident when screw it in tightly.