DO-204 is a family of semiconductor packages defined by JEDEC. This family comprises lead-mounted axial devices with round leads.
Generally a diode will have a line painted near the cathode end.
Several common packages are archived in DO-204 as variants, and may be referred to using their alternative names.
The DO-35 is a semiconductor package type. It is often used to package small signal, low power diodes such as 1N4148 (a 100V, 300mA silicon diode.)
The DO-41 is a common package used to encapsulate rectifier diodes. The name is derived from the JEDEC descriptor "Diode Outline, Case Style 41". DO-41 diodes are larger than signal diode packages such as DO-35, which are not required to handle large currents.
The most common diode using this packaging is the 1N400X series of rectification diodes.