A Plastic, metal or other material, incorporated into the paper sheet during its manufacturing process, fully or intermittently. A window thread appears on the paper’s surface at defined points, and is partially visible, however, in transmitted light appears across the entire length of the note. The thread may be able to contain any of the following: visible or machine-readable codes, microprinted or mini-printed text in positive or negative, or display of fluorescent, iridescent, holographic or... containing an invisible code printed in magnetic ink, which can be used to authenticate and/or denominate banknotes in Process of fitness sorting of banknotes by their condition of use. Through this process, used banknotes are classified as fit or unfit to return into the circulation. See Processing of banknotes. machines.