"Larry Jaques" wrote in message
...
On Fri, 16 Jan 2015 12:43:32 -0500, "Jim Wilkins"
wrote:

...
The standards are a compromise between the need for coarse tapped
threads in weak materials like iron and aluminum castings and fine
threads on screws to maximize the root diameter for strength. That's
why we have coarse and fine pitches. Metric standards are in between
and not ideal for either, as you'd learn fixing motorcycles.

One learns to use anti-seize on steel bolts going into aluminum
housings, too.

I've considered removing and coating the accessible fasteners when I
bought a new car, and decided against the risk of breaking a machine
that's under warranty since the torque specs in the shop manual are
for dry threads.

Instead I sprayed the engine and underside with LPS-3 in the hope it
would seep into the thread gaps enough to keep out water. Generally
they have loosened easily when I did need to remove them years later,
but a few hidden ones rusted and were much harder to remove.
-jsw