This adapter was made to hold up a 2 inch telescoping flag pole from Harbor Freight Tools.  The base is held in place with tent stakes and the upper portion clamps to the edge of a picnic table that is 1 ½ inch thick (standard.)  I printed this using PETG and tested it as shown, it worked great!  In addition to the 3d printed parts, you will need 3 tent stakes, two ¼-20 carriage bolts 2 ½" long, and two wing nuts that you can easily get at your local hardware store.