 Under one classification, treasury bills are categorised as ad hoc, tap and auction bills.Under another one, it is classified on the maturity period like 91-days TBs, 182-days TBs, 364-days TBs and also 10-days TBs which has two types.In the recent times (2002–03, 2003–04), the Reserve Bank of India has been issuing only 91-day and 364-day treasury bills.