This is the 'Monosling'; a slingshot that uses a single piece of tube rubber on a single mounting hole. 3D printable files attached, I have made a couple of these, and they work quite nicely. If you're not familiar with low profile slingshots I suggest using low power rubber until you are used to it, then you can upgrade to a stronger band (TheraTube Black is my preference).
To set the band to the handle, use the procedure in this video of mine: https://www.youtube.com/watch?v=tHP3uyxmMeo
And to understand how a single band sling works, Joerg Sprave has a good description here: https://youtu.be/HNuwxjBMDEU
To actually make the sling side, combine the style of Joerg's with the attachment method of mine.
My Patreon: https://www.patreon.com/jontheinventor