What are the rough opening (RO) dimensions for a knockdown hollow metal borrowed lite? The rough opening (RO) is 2-1/2″ wide by 2-1/2″ high. By Mary Mallis|2021-08-25T00:12:51+00:00August 25th, 2021|FAQs| Share This Post With Others! FacebookTwitterLinkedInWhatsAppPinterestEmail