On dial-up so loading from youtube is generally out of the question, so haven't seen this expander. Some years back I made a set of expandable 12, 16 & 20ga dent raisers. These have a split line straight down the center. Prior to turning I cut a groove about ¼" wide at an angle down the center of each half. A wedge then slides through the matching grooves. The wedge was made to just come flush with the end when un-expanded. Two brass pieces were made to fit onto 3/8" rods, one having solid end, the other recessed in the center for the wedge tip. In use the plug is centered under the dent & supported by the recessed piece from the tip & the wedge tapped tight from the other end. The dent is then hammered from the outside & plug can be retightened if needed for bad dents. When complete the solid plug is inserted in the tip side, the wedge tapped out which lets the plug collapse for removal. These have worked exceedingly well over the years for me, & have come through on several occasions.
