These nail sizing kits are necessary to purchase when ordering a custom sized set of press on nails. Simply pick the style of nails desired. We will then send you a sizing kit. Test the nails on your nail beds to see which number fits which nail. Write in what that number in the spot for each finger on the sizing kit. You will only need to do a sizing kit for each style of nail once. Your sizes will be kept on file. You need to do a sizing kit for any new style ordered. So for instance, if you have done a sizing kit for medium length almond, and you order long stiletto in your next order you will need to do a sizing kit for long stiletto.