Woodies, High elves, Halfies, and even Drow/Half-D.

Through their constant handling of all sorts of weapons and armor, ie Steel which has Iron in it. They are able to develop a small resistance or less of a vulnerability to their opposing metallic items.

This would only come from being very Intelligent and knowing where and how to touch such blades or what may cause the most damage in combat.

This would be similar to Keys to where they may be able to touch said weapons, sacrifice them, and get hit a little less hard by them but never wield them. Could have a stronger affect on Halfies as they have less blood from their counterpart Elf.