You are correct Bob, according to the SCR-221 technical manual
(TM-11-300) there should be two Bristol wrenches (#6 & #8) in the
spares kit. I have just tried the one I have on an old wreck of a
BC221-T and it fits but don't know whether it is a #6 or a #8. It
is just under a 1/10" across the flutes.

I believe that during WWII there was a specially employed
lady, complete with tattoos presumably, whose task it was to
tighten the set-screws on all military equipment. She did such a
good job that nobody except a certain candidate for the
governorship of California has since been able to move them.



I have seen the wrenches on e-bay from time to time.

To remove the screws after ordering a bowflex machine and working out with
it for 6 months, heat them and the "glue" will release and you will be able
to turn them.