1 of those blue heads was illegal/non-conforming. There is a designation to look for on the sole, but can't recall exactly what that is. Possibly a line under the name, but if that is it, I still can't recall which was the legal/approved version.
Ok. Just remembered that there is a version that does not have the patent numbers on the sole. Only the 7.5 was conforming, all others were non-conforming. And, they were hot heads!! The second version, with patent numbers, all are conforming.