Diamonds are a girl’s best friend, so when buying one for your sweetheart, you can gift it as part of a promise ring, engagement ring or wedding ring. If you are going to buy a diamond promise ring for her, you will probably not take her with you for the selection. Hence, it will be necessary to know about her finger size well so that you can buy a ring apt for her. Given below are three things to consider while buying a diamond promise ring for her.