The thread is embedded in (not printed on) the paper and runs vertically from the apparent area to your remaining with the Federal Reserve Seal. On authentic bills, this should be simply visible towards a light supply. Undetectablepropandcounterfeit.com has a wide variety of fake British pounds, UK funds, together with https://icelisting.com/story20451445/not-known-facts-about-buy-copyright-dollar-banknotes-100-bills-online