The lower is all put together and good to go. I do have one more question...
When I screwed it on to take a look how it feels, I noticed the lower half of the stock will not allow it to screw tightly in. Is there another part that I need to buy as well?
Looking at the last AR I purchased there is a threaded extension, so it appears.
Just installed my 1st UBR.
What did you screw on? There should be two things that screw in on the UBR install.
1. The buffer tube (entry receiver extension) should screw into the Lower receiver.
2. the screw that tightens the cheek piece (Main Tube assembly)gainst the lower receiver, trapping the detent pin and spring.
This is the only tightening or screwing that should be done in the assembly process.
Did you separate the stock body (lower half of the stock) from the Main Tube assembly before putting the main tube assebly on the buffer tube?