Credit card 4 starts with visa dual-currency card, 5 starts with MasterCard dual-currency card, and 6 starts with UnionPay standard card. If the dual-currency card is spent abroad, you can take the dual channel of visa(master) or UnionPay, and only the UnionPay channel can be used at the beginning of 6. To put it simply, when using cards abroad, there are more cards starting with 4 or 5, and the standard cards starting with 6 can only take the UnionPay channel, but the cost is relatively low. It doesn't make much difference if you only use the card in China.