[LMH]

The drive nuts on my Hurricane were Trigo and used an Allen wrench to tighten the nuts. Seems to me with my extremely poor memory, that Kirkham did make some shorter with a hex on the outside. That allowed the stud to protrude farther into the nut allowing it to be shorter. Was a long time ago though.
I think it was kind of experiment David was doing and not a regular item he produced. Might try calling him and asking.
Larry