[Healeys] purpose of brass nuts

[goldengt at cal.net]

Yesterday, I saw three hairline cracks in my intake manifold at the flanges. The last time I had the manifold off, I decided that the factory brass nuts were sort of tall and giving a little extra grief during header installation gyrations so I used plain steel nuts. Does someone know the purpose of the brass? Corrosion resistance is all I can think of.
I am having the cracks welded.
Thanks,
Ken Freese
65 BJ9