Since the early 1920s, the most common monetary policy tool in the US has been:

1. Several tools are available to a central bank. 2. One of them has dominated practice for a century. 3. The most common monetary policy tool has been open market operations. 4. They involve buying and selling government securities. _Source: OpenStax Principles of Macroeconomics 3e (CC BY 4.0), Ch 15 'Monetary Policy and Bank Regulation', sections 15.1-15.5_