T-bills (Treasury Bills), SDLs (State Development Loans) and Government bonds are all types of Government securities, but they differ in several key aspects, such as the issuing authority, maturity period, purpose, and level of risk. Here's a breakdown of the differences between them:

Aspect	T-bills (Treasury Bills)	SDLs (State Development Loans)	Government Bonds
Issuing Authority	Government of India	State Government of India	Government of India
Maturity	Short-term maturity periods, typically ranging from a few days to one year.	Medium to long-term maturity periods, ranging from a few years to a couple of decades.	Longer-term maturity periods, often ranging from several years to several decades.
Interest Payout	On Maturity	Every 6 months till maturity	Every 6 months till maturity
Bidding window	Mon - Tue, every week	Mon, every week	Tue - Thu, every week