Why different buffer tube sizes?

[andyems10]

I don't know if I'm in the right thread or not for this but here goes.
Why are there two different types/sizes of buffer tubes for ARs (Commercial & Mil-spec)? Is one better or stronger than the other. Just seems more simple to me for all of them to be the same to make part ordering easier. I noticed that all S&Ws come with the Mil-Spec and seems most others are commercial size.
Anyway, it's nothing really important that I need to know for anything specific. I just don't know the history behind the different tubes and just wondering. Thanks in advance.

 

[Kodiakco]

I've read it cost more to make milspec type but can't confirm it.

The biggest differences between the two tube types are: 1) The buffer tube diameter itself 2) The diameter of the threads in relation to the diameter of the tube.

Mil-Spec: On the mil-spec buffer tube… the threads at the front are actually a larger diameter than the rest of the tube itself. In manufacturing, a large tube is used and threads lathed as normal. Next, the rest of the tube must be milled down to the military specified diameter. I’m guessing this step requires more work / precision… and costs more.

Commercial-Spec: In manufacturing, you begin with a tube that matches the final tube diameter. The threads are cut into the front end with a lathe just like any other threaded pipe. I imagine this to be just like the copper water pipe used in my house. Cheap & simple.

 

[MichiganScott]

Ease of manufacture of the commercial tubes. Notice on the pictures above that the commercial tube threads are the the same diameter as the tube, while the mil-spec threads are larger than the tube.

Supposedly using a screw machine to manufacture the threads on the commercial tube weakens it.

 

[TangoFoxtrot]

The mil-spec seems to be better built to me.