Lens hoods can become loose over time, leading to annoying rattling sounds or problematic vignetting if the hood rotates into your shots. Instead of buying a replacement hood, you can apply a quick fix using a little tape or glue. Simply cover the threads with a few layers of tape or a few dabs of non-permanent glue (be sure to wait until it dries). The extra material around the threads should help the lens hood to secure much more tightly to your lens.