When I bought my GBSE I had to get the 11" DD coil from a third party, no names but the seller believed that all the coils were the same at that time. My coil says teknetics on it,not fisher. I dont see any other marks on it,no part number etc... I dont mean to ask stupid questions,but how do you tell a 11"DD F75 coil from a 11"DD GBSE coil???? I need to know if I have been using the wrong coil for 6 months. That would suck, and I'm really curious today because yesterday I used the small coil that the GBSE came with and found several old coins.