Galling? I have always presumed that galling must mean as I thought,
bending or deforming screw threads by excessive strain, as I saw once
on a turnbuckle screw which seemed ready to skin itself of thread and
slip out of the bottle screw like an exhausted stallion.

So I looked it up and find nothing on my Pocket Oxford about metal
galling, only insect caused galls or swelling, or emotional upset, or
digestive juice, or rubbed bare spot on horse. I seem to recall mother
used it as in effrontery, or guts. It seems as if insult is included
with galling, so if excessive force is insulting to metal, then the
gall might show as deformity, as with my old backstay adjuster, starved
of oil. (Not my fault!)

Mounting deck stuff must first provide a mechanical base, then seal the
gaps and threads with polysulfide, or white lead, or something that can
be removed and reworked. Best replace deck core local to hole with
epoxy, then bed with something. I used foam O rings which were touted
to seal threads when compressed, but that was 30 years ago on a plywood
boat I sold after a year at a profit. I don't know if it leaked later
on, or not.

If some resilieance in the mount is preferred, rubber mounts would be
in addition to all above. If the resilience is relied upon heavily,
expect to rework the monkey often.

When driving screws into fiberglass, one is better to tap thread in
first. Heavy loads and thin glass call for backers, nuts, washers, etc.
Alternatively, use self tapping screws, or make your own by filing a
tooth or two into the screw end with a triangular file.

Repetitive partial insertion and removal will allow air blast
evacuation (close eyes and blow!) of glass powder in short blind holes
formed by thread cutting which will wad up the process. Might better
use a thread tap if the right size is available, but this works.
Threads wick, so a little wax or other sealer should be used, if a
possible slow drip is unacceptable.

There may be talk of deoxidised water and crevice corrosion, not my
speciality.

While learning how to file the right angle on the teeth, I galled
myself by breaking an ss screw off flush with the surface. If the
screw was galled too, it was justified. I would pump up robertson screw
heads for this operation.

Terry K