Not sure what the problem is then. But I know my castle nut bottoms out, cannot torque (or really even tighten). All 4 TRE's wiggle a good amount. So something with fitment is off. I'll prob take actual measurements in a few days with a caliper.
Theres either a fault with the TRE's or the taper hole in the arm is too deep. For reference, the taper should be 1 in 10, ie the hole grows 1 inch in diameter in every ten of depth. The small end of the hole should be 14mm if your using fj80 TRE's so that as soon as the thread ends it should be pulling at the taper.
Have you tried using washers under the castle nut to avoid bottoming out the threads?
Did you sell that arm?
