Installing Collapsible Stock

[JNA]

Hey Guys,

I am having a bit of problem installing my collapsible stock on my new AR180b. I think its a problem with the buffer tube itself or some of my own incompetence. Now before I bought anything i contacted Stormwerkz regarding the AR180B type 2. They told me:

The threads on both commercial and mil-spec are the same so either will work.
The diameter of the tube where the stock slides is where the difference is.
You will need the stock, receiver extension tube(buffer tube), castle
nut. Usually less expensive buying a complete stock kit.
-Josh

Now I believed them and went with the Rainier milspec buffer tube and according Magpul CTR milspec stock. However when I installed my stock mount and tried to put the castle nut that came in with the Rainier buffer tube it appeared that the castle nut would not pass the first set of threads shown in the pictures:

Now I tried to fit the butter tube into the stock mount and it as well would not fit. Now my question is my buffer tube out of spec or do I need a commercial buffer tube. Any input would be appreciated.