As soon as I get my Colt LE6920, I'll be adding a side sling mount.  I'm new to AR's and am wondering what's all needed to remove the stock?  Is it just the CAR spanner wrench?  I heard that Colt uses different castle nuts than everbody else, is this true?  Should I switch?

Best place to buy the tool?

Sorry for the definite newbie questions! Thanks for your help.

Well, you're probably going to have to wait until you actually get it before you buy the tool.  

However, I can tell you this: if the castle nut is the one that has 4 square shaped "divots" cut into it at 12, 3, 6, and 9 o'clock, then you will need one of these

If its the other one, with round holes in it, you will need one of these (actually, only the hook looking thing on the left end)

Good luck

No matter what nut is on there.... the plain old standard $6 CAR wrench.... is all you "need".  The other RRA castle wrench just makes it easier.... IF you get a castle nut.

Thanks for the help guys.  Much appreciated!