Speaking of rusty balls…..
On one of my caps, I could not hold the cap in the vise with
my soft jaws, or wood scraps without destroying the cap
while trying to unscrew the insides, so I ended up drilling
a couple of holes in the top of the cap to hold it in the vice
with a make shift spanner wrench.
I ended up alumi-brazing the holes up, and sanding down,
and polishing the cap, and the holes were barely noticeable.
Hopefully when you find a cap, it’s in better shape.
Prepare to be boarded!