Difference between "Commercial" and "MilSpec" parts??

[baglock1]

It is also worth clarifying that although the mil-spec is shown to be a 4-position and the commercial spec is 6 (i.e. the holes on the bottom side of the tube), 6 position tubes can be had in mil-spec diameters.

[Irving]

So commercial stocks can be used on both tubes? I assume mil-spec stocks only work on mil-spec tubes?

[Mazin]

Mil spec stocks only fit on mil spec tubes. I haven't tried a commercial stock on a mil spec tune but if image it would work but you might have a lot of rattle, as well as the possibility of some position missing.

[Circuits]

In reference to stocks, it's only about the tube diameter anymore. Most so-called "milspec" tubes are just the smaller diameter, and still use cut threads and the wrong alloy, and don't follow the milspec for heat treatment and finish.

True mil-spec is 7075T6, same as the lower and upper receivers, made from a forging, with rolled threads and milspec dry lube finish.

"mil-spec diameter", often incorrectly advertised as "mil-spec", uses an extrusion, cut threads, and whatever finish the maker thinks is inexpensive enough. They can be had in good old 6061 or 7075.

Most people just care that their stock body fits nice and snug, and there's nothing wrong with commercial tubes be they in the old big diameter or the "mil-spec diameter".