ΔE 33.4, loose: different enough that you should pick on purpose. Brass is noticeably darker, much more saturated than Iron Fist.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 33). Brass is noticeably darker, much more saturated than Iron Fist.
The same difference applies the other way round: Iron Fist is noticeably lighter, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Iron Fist on the colour wheel See Brass on the colour wheel
All matches: Iron Fist equivalents · Brass equivalents