Buffer Tube Question Mil-Spec vs Commercial

Sorry if this has been covered before but the search function is not cooperating.

My question is how can you tell the difference between a Mil-Spec Buffer tube and a commercial one?

I would think they measure out differently and if so what is the spec’s to identify Mil-Spec from commercial.

Thank you.

I have always been curious about this so I am taggin this post to follow it.

Did you use the orange search button at the top?

http://cdn.magpul.com/downloads/Receiver_Extension_Comparison.pdf

Yes I did hence the “search function is not cooperating”

Thank you for the link as it answers my question.