The 1N400X series of diodes are general purpose rectifier diodes. The last digit, from 1 to 7 indicated it's rated voltage.

1N4001 = 50V
1N4002 = 100V
1N4003 = 200V
1N4004 = 400V
1N4005 = 600V
1N4006 = 800V
1N4007 = 1000V