Constant Content

So is it:

"social security number", "Social Security number" or "Social Security Number"?

The Carnegie Mellon writing resource says to use "social security number" and only to use capitalization when referring to the Social Security Administration. I checked the OWL as well. Although it does not provide any guidelines for actually writing it, it does use both "Social Security number" and "Social Security Number" when referring to paperwork students need for various enrichment courses.

So now I am truly confused. I want to write it out the correct way in my article. How do others here refer to the SSN in articles?

It is written as Social Security number on the Social Security web site like this:

"A dishonest person who has your Social Security number can use it to get other personal information about you. "

This makes the most sense to me since "Social Security" is a proper noun/institution and not a generic term like grocery store. Hopefully, the SSA knows how to write its own terminology properly.

The AP Style Guide says this about Social Security:
Capitalize all references to the U.S. system. Lowercase generic uses such as: Is there a social security program in Sweden?