An index used to establish interest rates for adjustable rate mortgages. It is based on the interest rate paid to private investors by the US Government to obtain funding for the national debt and other expenses. Sometimes called T-bills, they are available in denominations of 3-months, 6-months and 1-year. The 3-month and 6-month Treasury bills are auctioned every Monday, and the 1-year Treasury bills are auctioned on Tuesday. The resulting figures are released to the public the next day. This index can have either a weekly or a monthly value.