[Mgs] Why brass?

[Simon Matthews]

After successfully disassembling and reassembling the throttle shafts,
I progressed a litle further. Because the nuts that hold the manifolds
onto the head had been loose, I proceeded to replace the gasket that
goes between the head and the manifolds.

Unfortunately, two of the studs came out of the head, instead of the
nuts coming off the studs. I have ordered replacements, but I noticed
from the catalog that these nuts are brass.

Why are these nuts made from brass?

Simon