USPS Eastern Tiger Swallowtail - Sheet of 20 stamps (two-ounce Forever stamps, greeting card, square envelopes, Wedding stamps) For use on irregularly sized envelopes, such as two-ounce letters, square greeting cards, invitations, announcements The square format of the stamp was developed in partnership with the greeting card industry specifically for over-sized or square envelopes Sheet of 20 stamps Non-Machineable Surcharge stamp is always valid for that rate (68 cents as of 4/10/16), similar to a forever stamp Can also be used on any USPS mailings, value applied towards total postage cost