This eyepiece was designed for the TSN-660 series spotting scopes. But it will also interest owners of the Original Kowa TSN-1, 2, 3, or 4 spotting scopes. If you're in that group, and always wanted a good quality zoom eyepiece, then the TE-9Z fits perfectly and performs really well, especially with the Prominar versions (TSN-3 and 4). An excellent all-around eyepiece for the TSN-66mm scope. Note: does not fit TSN-770 / 880 Series spotting scopes. Will fit TSN-1, 2, 3, 4.