I had a metal loop, with the little flat part behind the string that the knock slid over. The think I hated the most is that if the loop got twisted a little one way or the other, the arrow would pop right off. Often times when I am sitting in my treestand, I hold onto my bow, and have my release clipped on the string (loop). With the metal loop, every time I turned my release to the side or something while I was sitting there, the arrow popped off and fell to the ground! Not fun at all!