Indentification of INOX versus brass part?

[DarrellBash]

I'm servicing a MK10 regulator (not a MK10 plus) and one of the schematics has two different torque settings for the swivel retainer. It's 4 n-m for brass and 8 n-m for INOX. I am reasonably sure that this MK10 is brass but is there some way to tell for sure? Thanks!

 

[Popgun Pete]

You could try a magnet, although some stainless steels are not magnetic. Another way is to check the surface finish with a magnifier as brass is polished before plating and that rounds off any edges, whereas stainless steel is just the machined finish. Hardness is another test, but that involves marking the item with a punch. Looking at the internal threads the plating may be marked or incomplete at the back of the thread.

 

[herman]

The easiest way is to do a scratch test. On the flat surface opposite the threads, simply scratch the surface with a steel oring pick then examine the scratch. If you see brass color, it's plated brass, if not, then it's stainless steel (INOX). This surface has no sealing function and is inside the regulator so it does not show or cause any corrosion issues.... or you can simply torque the bolt to the brass spec and be done with it. The torque in and of itself is not important as long as the bolt does not come loose during use. Considering the mating surface is brass and fairly thin, I would use the brass torque in either case.