On Thu, 18 Jun 2020 14:55:29 -0700, Bob La Londe
wrote:

On 6/18/2020 4:09 AM, maxq wrote:
I'm making a special tool out of a 3/8 drive socket. It'll have to be
turned by a wrench or gripped by vise jaws. I'll file flats on the
square end.

Should the flats be parallel with the square's sides, or have the point
in the middle? This is a high-torque situation.
High torque?

Start with a quality impact socket, have a hex ground on it, and use a
top name tube wrench. I suspect anything else would be an exercise in
frustration unless you can find an appropriate socket that already has a
hex on it like some spark plug sockets. I would probably not use an
actual spark plug socket. They might make one that can handle more, but
torque specs on plugs are pretty low. Why borrow extra risk on what
sounds like an trapped installation.
You got one of those 12 spline 20mm antiques?? Try a 3/4" AF coupling
nut drilled out to fit over the axle if necessary - I believe the
coupler nut for 1/2" allthread is 3/4" 20mm is .787 so it is about
..030" smaller but it might kust be big enough to grab 6 of the 12
splines and get it off.