Robby: the threads not the head.
Acksaw: did you compress the spring first? It is sometimes to long and too stiff when not compressed first. So maybe it had just two threads in but too much tension. I dont have any tension on the first two threads.
You can use a Associated screw diff nut set too, that should be enough if you didnt run it jet.
10th can be a bit frustrating at the beginning
but ball diffs are great and easy once know how to set them and how to build them.