Strange reading from rectifier

This is difficult because the 1N400x series of diodes is made by a number of different manufacturers all of which seem to have different component marking conventions.

ON-semi have a 3 line set of markings with the full part number as the second line.

Fairchild have a 2 line marking again with the part number in full.

Other manufacturers do not seem to specify their markings.

Edited to add

Now that you have added the picture it does not look like a 1N4006. The normal package for the device is a DO-41 which has a body length of between 0.16 and 0.205 inches. Your device looks like it is 0.1 inches long.

Kortuk stated it correctly, 120cps for Full Wave, 60cps for Half Wave.

As a side note, but seldom taught in books or schools.
Unless you need High Voltages, like a Tesla coil.
Avoid designing a resonance filter, or harmonics thereof, as very high voltages can develop.
The voltage developed is from circuit 'Q', at resonance, not just turn ratios.