To use this, tighten it to the size you require and make sure you can remove it over your knuckle. Please be aware that fingers can change in size throughout the day depending on the time of day and the temperature. I would recommend that you check the size a few times in a day to make sure you are ordering the correct size. We cannot guarantee the accuracy of these plastic ring sizers which is why we recommend using a jeweller - most high street jewellers can tell you your ring size free of charge.