The lid has the basting "dimples" that go in vs. the basting "tits' that stick out. The bottom of the skillet has a size that is 10 5/8. The only foundry I've seen use fractions on the diameter is BSR. Also, if you look at the shape of the handle of the skillet, the bottom will be a V- shape up to the body of the skillet. Don't sweat it Mike, over time you just get to know what they are by looking at them. The shapes and markings are different and eventually you'll be able to tell them apart just by looking.