As you can see in the picture below, ball-end strings (top) have a brass "ball" in the end. Loop-end strings have a twisted loop.
Those of us who build instruments never use Gorilla glue -- it expands and has a tendency to open cracks. Likwise we seldom, if ever use epoxy. For hairline cracks which can be opened by pressing on one side or the other of a crack, we us a cyanoacrylate (Super) glue. For cracks which need filling, we use a mixture of fine sawdust and Titebond or Titebon II, I often run a bead of the glue into such a crack and then sprinkle sawdust on top,. Then press the m