T mount vs T-2 mount

T mount:

Tamron introduced the T mount back in the late 1950’s as a potential “Universal” lens mount. The T mount is a threaded screw mount, has a 42mm diameter 0.75mm pitch (M42x0.75). 

Similar to the Pentax M42 screw mount, but with finer pitched threads. The Pentax screw mount is a 42mm diameter screw with a 1mm pitch (M42x1),

T-2 mount: which is simply the name that Soligor used for its version of the T-adapter. 

A T-adapter consists of an inner ring with T-mount thread and an external ring with corresponding lens mount. The T-ring and the T-2 ring are identical to each other. Both of them have the inner and outer ring. The two rings (inner and outer) are held together by 3 peripheral screws on the external ring. Loosening these screws allows rotation between the lens and the camera body. This is especially useful when the camera body is attached to telescopes or microscopes.

Registration (flange distance) on a T-2 mount is 55mm, to allow room for the adapter, and still match up with virtually any camera. 

wiki

T mount and T-2 mount are interchangeable