Materials needed for this are as follows:
-dremel with diamond cutting disc
-saw to cut small wood stock
-Carriage bolts or hex bolts
-drill with drill bits
Step 1: Planning your cuts
Depending on the thickness of the material you are going to be using, helps determine your cut depth and size.
You can use what ever size wood or stock for the lower cut on the tube. This cut must be matching on the other side of the tube as it will be holding stock.
Step 2: Cut and drill
Use a metal file and some sandpaper to ensure the wood for the eyehole fits snug but removable.
Drill a whole the size of the carriage bolts that starts about 1" from the corner of the tabletop and goes threw to the wood into the wood in the eyehole.
Countersink the hole that was drilled on the tabletop of desired.
Remove wood from eyehole and complete the drill if needed.
Attach T nut on the underside of the wood for the eyehole.
Test out the fit once again except this time with the carriage bolts in.
A quick drawing demonstrates a sectional of how the cardboard tube (leg) attaches to the tabletop surface.
By putting a T nut on the bottom of the wood stock in the eyehole, allows for a clamp like bond when the hex bolt is threaded from the top of the tabletop surface.