The 1N4001 series (or 1N4000 series) is a family of popular 1.0 A (ampere) general-purpose silicon rectifier diodes commonly used in AC adapters for common household appliances. Blocking voltage varies from 50 to 1000 volts. This diode is made in an axial-lead DO-41 plastic package.
The 1N5400 series is a similarly popular series for higher current applications, up to 3 A. These diodes are typically available in the larger DO-201AD axial package to dissipate heat better.