Sean, it screws on the threaded part on top of the pole and the AT has a screw thread in top of it to screw an angle joint on.
Jonboy, you may have got one of a small batch I made deliberately tighter as people were saying they were too loose to begin with. As standard during assembly I use a small amount of silicon grease which makes them a little looser than normal for the first week or two, then tightens slightly. I thought I could get round this by making them that little tighter to begin with, but they ended up too tight. Its worth opening it up and putting a touch of grease on the O'rings.