using threaded rivets?

[rdykiel]

Hi
I had to remove the boom bracket of a rigid boom vang. The backet was held to the boom via SS machine screws that were going through what appears to be threaded rivets fastened to the boom. I need to replace a broken rivet and was wondering if I should choose SS, aluminium, or another metal for this application. Also, do you know a good provider of threaded rivets?
Thanks