Gold Bullion Bars, Rounds, amp Coins. Gold Bullion Bars . A flat bar struck using .999 usually pure gold is known as a gold bullion bar. Ranging from 1 troy ounce to even 32 troy ounces, gold bars are available in various sizes. However, 1 gram, 1 oz, 100 gram and kilo size remain the most common weights available in the bullion market.