999 standard clutch basket material

I took the clutch plates out for inspection and realised both the friction plates and basket are non magnetic which must mean they are aluminium, are they normally steel from standard?

It appears the previous owner must have replaced the basket at some time if that is the case, unless the standard isn't steel and some other non magnetic material (Magnesium/Titanium etc?)

 

Thanks for that link, I'll order some new Newfren alloy ones now I know what they are made of.