I think they are 12x1.25. I've got some closed end long acorn nuts for mine, and I'll check the thread for sure. You'll need some way of turning the die without a die wrench, like a big deep socket, so you can bottom the socket against the flat axle flange to keep it square. If you have one of those useless 1/2" drive sliding bar tee handles, here's the chance to use it. I'd mail you mine, but it's now a tee jay driver (excessive use of cheater bar), and it'd be sacrilegious to use a Heep tool on a Monty...

Not responsible for advice not taken...