yeah, i know, but have you noticed that the "genuine" are NOT steel ?
you call steel to anything that is metallic ?
Taga is genuine BMW manufacturer - that's no doubt. So, i guess, i was wrong thinking that there was no aluminium version.
I showed the full list - to show that is hard to say if aluminium catches are genuine exactly for E9 (2.5CS, 2800CS, 3.0CS, CSI, CSL), not for NK - 2000C, 2000CA or 2000CS which are not E9.
Maybe aluminium catches as Gransin mentioned where used in NK or very early 2800CS & later where replaced with steel version because of cracking or some other reasons (that is just my theory).