COMEX sets the world's benchmark futures prices for precious and base metals and publishes the daily vault report that splits inventories into registered-and-eligible stocks. Delivery is by warrant against metal in approved New York-area depositories.
Long-running arguments about "paper gold" come from the ratio of open interest to registered metal, though in practice the vast majority of contracts are closed or rolled rather than delivered.
Example: one COMEX gold contract (gc) is 100 troy ounces; silver (silver-futures) is 5,000 ounces; copper (copper-futures) is 25,000 pounds.
Related: cme-group, gc, registered-and-eligible