I've resorted to using giant C clamps to tighten them against the arm. That did the trick.He said "jabronis".... Cool.
Tec question: anyone have good ideas how to keep a TRE from spinning while tightening down the castle nut. The TRE spins and won't allow me to get the nut down. I've cleaned it up really well and even tried chalk to give the TRE something to bite...