butt stock tubes?

[turbo-minivan]

ok, i have a S&W MP-15 with a commercial butt stock 6 position tube on it. i bought a magpul stock for it and mistook the commercial for a milspec. so i now have a milspec stock that wont fit my commercial tube. the question is, it is cheaper for me to buy a new tube than a new stock, but are all lowers threaded the same to accept either size tube? are the threads the same? can i buy a milspec tube and thread it onto my AR in place of the commercial tube without any issue?? kinda confused.
thanks.

 

[NorCalDustin]

This should also help to show you the size differences (NOTE: Sometimes the commercial's do not have the slant back there)

So, because the threading part on the milspec has a greater diameter... You cannot put a mil-spec tube in a commercial lower.

The good news is, normally commercial stocks are slightly cheaper (as are the tubes because they are easier to make)...

 

[Urban_Ops]

Both share the same threads: 1-3/16x16
The crest of the threads on the commercial will normally have flats on them from being smaller diameter but otherwise the same thread and interchange with no problem.

 

[turbo-minivan]

thanks guys. thats what i needed to know.