These are towhooks large and small for launching model aircraft on a bungee launcher.
I use the small one for smaller wings such as a Pinata or the Caipi (about 1kg AUW)
I use the large one for my Chimera. (2-4KG AUW)
They are designed to attach to a key ring, The small one to about a 1" and the large to about a 2" ring.
Be sure to mount these to a structural area of your plane about 2/3rd's the distance from the nose to the CG on the centerline. And rough up the base of these printed parts well so they accept the glue. I use GOOP to glue them to foam. I also like to carve out a square into the foam and sink the printed part into the foam for added strength of the bond.