OOK has been used by art galleries and museums since 1964. The Perfect Hang kit includes 30 lib wire, ring hangers and reusable blue steel nail and brass collar. Center-of-gravity nail guides eliminated loose hanging and a reinforced elbow allows added strength. The ultra-thin nail minimizes wall damage by making a tiny hole. Choose a weight rating that exceeds the object to be hung. Weight rating is based on hanger nailed into stud and is not cumulative when using multiple hangers.