Even SS will attract a magnet (a bit weaker except for 304 & 316 alloy which are non-magnetic)

O like the idea of brass plumbing caps (natural gas?) that screw onto a brass/steel (NPT MxMxF) "T", but I don't know how the weight balance would be.
One could swap out with iron caps when needed, but then again who would take the time to do that? I'd just make a pair of hammers, one in each material.