Brass or white metal are most common, but a few of the HI models often come with steel fittings. You can tell by the magnet test.
I'm not sure what is "normal" for the Thamar dui chirras, but I just got one from the 7/11 DOTD where the bolster, buttcap and keeper are all steel. I like that.
It means that for maintenance you should use mineral oil or whatever you use on the blades on the fittings as well.
I should add that my new Thamar dui chirra was listed as 18.5" OAL, but is actually 19.25" OAL. It's a nice weight at 27oz, and the fullers are deep and perfect. In fact the whole knife is perfect, and the highly curved handle is very comfortable. It has that extra detail on the cho that only Thamar is doing these days.