What is the role of gold, silver, copper and iron bars in heavy machine gun soldiers?

In the game "Heavy Machine Soldiers", the roles of gold, silver, copper and iron bars are as follows:

* Gold bars: you can sell money.

* Silver bars: you can sell money.

* Copper pole: it can be sold for money.

* iron bars: they can be sold for money.

In short, these metal bars can be sold in the game in exchange for the money in the game.