According to Brent Philion :
Is it just mild steel or something a little more resisitant to oxidizing?

Just wonder if anyone knows off the tops of their heads

Copper! Modern ones often have a coating of iron over the
copper, to control the slow dissolution of the copper in the lead/tin
alloy of the solder.

And -- those are sometimes coated with gold over the iron, to
prevent corrosion of the iron before it gets tinned.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---