I have a friend at work who recently bought a colt one piece upper and noticed his barrel nut was loose.  He is fairly new to to ARs and my combo AR wrench obviously wont fit.  Where should I point him to get the appropriate wrench for his rifle?  When he first described to me the issue I thought it was a setup like Mega's monolithic rail, with the tube style wrench, but the bottom portion of the rail comes off to access the nut.  I feel like I have seen a small spanner style wrench that is for this purpose but I cannot find one in my brief chance to search at work today.

Thanks in advance.

Check with brownells they did have a wrench for it...

that's the one!  Thank you.  Sucks that it is so expensive, but a quick search through the archives shows that this is not a new issue with the 6940.

I imagine that Adco might be a little cheaper than buying the wrench.
Adco has the proper tools and experience to work on a 6940, and I would bet they could tighten your friends barrel but for a reasonable price.