Hi Leesa, we installed the hooks before the mirror was put in place. In case of a very heavy/large artwork a blocking inside the wall would be good to have. In some instances a cleat is better than hooks, especially if blocking is not possible for the large and heavy pieces. Once the appropriate hanging device is decided and installed the measurements for the mirrors can be taken. Such mirror has the cut out openings where the hooks or cleats are located. I hope, this will be helpful. Ania