Coins, also known as Industrial Credits, can be crafted by placing four Refined Iron Ingots in a square shape. This will create 16 Credits, a rate of four Credits per Refined Iron. These Refined Iron-tier credits can then be downgraded by placing one into a crafting grid to create eight Copper Credits or upgraded into a Silver Credit by placing eight Industrial Credits into a Crafting Table. Eight Silver Credits can then be upgraded to one Gold Credit and eight Gold Credits can be upgraded to one Diamond Credit. Thus, one Diamond Credit is worth a full eight stacks (512) Industrial Credits, or worth two stacks of Refined Iron.
Conversion recipes between Credit tiers are shapeless; however, the crafting of the original Industrial Credits and conversion from Credits to Refined Iron is not. Conversion rates between the different Credit tiers are non-lossy; converting up or down will always retain the same Credit value. However, if Industrial Credits are crafted back into Refined Iron, more than 50% of the iron used in crafting will be lost. This makes Industrial Credits a highly impractical way of storing Refined Iron.
Industrial Credits have only one purpose: they are used as currency on multiplayer servers. Industrial Credits are not used in any crafting recipes, machines, etc. Due to the lossiness of the conversion of Credits back to Refined Iron, it is highly inadvisable to create these on a singleplayer world, as they serve no purpose and would only cause the player to lose a considerable quantity of Refined Iron used in making them as well as time spent converting credits up and down as would be necessary to store credits within any reasonable storage space. However, in the GregTech, there is an option to enable/disable Industrial Credits to be found in dungeon chests. This option is disabled by default.