Proverbs 27:17 - Iron sharpens iron; so a man sharpens his friend's countenance.
Jeremiah 17:1 - The sin of Judah is written with a pen of iron, and with the point of a diamond: it is engraved on the tablet of their heart, and on the horns of your altars;
Jeremiah 15:12 - Can one break iron, even iron from the north, and brass?
Jeremiah 11:4 - which I commanded your fathers in the day that I brought them out of the land of Egypt, out of the iron furnace, saying, Obey my voice, and do them, according to all which I command you: so you shall be my people, and I will be your God;
Job 41:7 - Can you fill his skin with barbed irons, or his head with fish spears?