i do have 6" vernier calipers and never thought of measuring from the top.
Anyway my rotors are 5.96" at the top and BJ's are 5.942" so i'm close?
My caliper jaws are not deep enough or wide enough to measure the hat at the bottom.
Well, the top is pretty much the same as my original rotor, so that's good. But, it all depends on how wide the taper is at the bottom as well. I just went out to the shop to check the new rotors (that rub) that are pressed onto the hub. Unfortunately, I can't get an accurate reading because the hub gets in the way of the calipers, and the caliper arms are too short to reach the hat over the hub. Maybe I should have bought an even bigger caliper from Amazon!