Purge plug for back purging tube for Tig Welding. The outside of the plug will fit a max tube 2.5" ID down to 1 7/8" ID

The inside of the plug is tapered to fit the outside of smaller tubes. 1.5" OD down to 1.25" OD
Pretty basic but works well, stays put with a few gentle taps. Just need to keep tube temperature in check near the ends. Resize to suit your needs.

I print with a wall line count of 4 or higher which gives some extra room for drilling the center hole to different sizes, and helps to keep the tube from causing the outside of the plug to fail.