The interchangeable T-Mount system was popular around the 1960's before Tamron introduced the Adaptall mount. T-Mounts attach to the lens via a 42mm thread with a pitch of 0.75mm, as opposed to the 1mm pitch of the M42 lens mount. Now I've recently acquired a couple of what I think are T-Mount lenses, but the mounting thread is larger, more like 46mm. Is this still classed as a T-Mount? And are the larger thread T-Mounts available anywhere? Thanks in advance.