I see that they do now but I have had these cards for a couple of years and they don't have the class written on them. An old order email I had said that they were class 6 which is why I said that. I should also have said that these two cards work fine on my tablet and S3.The class of the card is written on it, in an incomplete circle. As far as I can see from pictures on the net, Mobile Ultra cards are class 10 AND UHS-1, which seem to cause problems.