Wire
noun
A needle made of gold is a wire. Perhaps wires were made from gold mostly back in the day? And they were thin like needles? That's my guess.
The reading is the kun'yomi reading of both. You already know both of these, just watch out for the rendaku on 金!
針金が床に落ちていたよ。
The wire was on the floor, you know.
針金を使って留めましょう。
Let's use a wire to fasten it.
これはハンガーの針金を曲げて作ったアートです。
This is art made by bending hanger wire.