Types of T-Bills
In the US markets, though there are many types of T-bills, they can be broadly classified into two types - regular-series bills and irregular-series bills.
Regular-series bills are issued routinely by competitive auctions, either on a weekly or on a monthly basis. These bills are issued in regular series. They are issued by Federal Reserve district banks and their branches with different maturities of 3 months (13 weeks), 6 months (26 weeks) or 12 months (52 weeks). New issues of three or six month bills are auctioned weekly; whereas, new issues of one year bills are normally sold once in each month.
Irregular-series bills are issued when a special cash need arises for the Treasury. These T-bills are of two types - strip bills and cash management bills. Strip bills are nothing but a package of bills requiring investors to bid for an entire series of bills with different maturities. Investors who bid successfully must accept bills at their bid price each week for several weeks running. Cash management bills, on the other hand, consist simply of reopened issues of bills that were sold in prior weeks. The reopening of a bill issue normally occurs when there is an unusual or unexpected treasury need for more cash.