The 1N4004 is a standard recovery rectifier diode from On Semiconductor. It features a 400V peak repetitive reverse voltage and 1A average rectified forward current.
The 1N4003 is a 200V, 1A standard recovery rectifier diode from NTE Electronics. It features a forward voltage of 1.1V and a surge current rating of 30A, housed in a DO-41 through-hole package.