Review on Flap Discs PCS 4 5 Inch by Eric Temple

I got a stack of 40/60/80/120 for a welding school. They don't supply them to us, but we really need them. Used Pad 60 this semester to set up crafting and MIG boards. I've probably used this mat for maybe half an hour total and it's already half used. When they arrived in the mail they were shrink wrapped as shown in the picture. Every tenth pad had a small piece of paper showing grain size. As far as I can tell there is no other measure of granularity. Heck, as far as I know they can all be 40 grit.