What are the differnce in dimensions for the commercial and mil-spec buffer tubes?  Do they both have the same OD?  Are they different in lenght?  My S&W M&P-15 buffer tube has a 1.15" +/- OD.   Anyone know if that Is a commercial or a mil-spec tube?  Thanks

If your tube measures 1.146 -1.148" it is a mil-spec tube. Also, the threads on a mil-spec tube are rolled into the tube whereas they are cut into a commercial tube Commercial tubes measure 1.168 -1.170" and usually(not always) have a slightly angled /slanted back end.

Note: Not all mil-spec tubes are created equal. Some are mil-spec in dimension only, and are not made of the proper materials.

I am more of a picture person

In a pinch would a commercial CTR work on a Mil-Spec buffer tube because of the way a CTR locks up tight, or still too loose?

Yes, the commercial CTR will work on mil-spec tube.

How do I know, my local dealer put a commercial size CTR stock on my shopping bag, and I already told him I need a mil-spec size because I have Colt/ LMT/ Vltor mil-spec size tubes, he still grabbed the wrong box.

When I got it home it fitted snug when the friction lock is on, but very loose when it's not locked, then I noticed the box said commercial model.

My dealer when he found out sent me by express mail a mil-spec size stock with a free return postage in the box which I got the next day, not too bad but I learned a little something.

Thanks