A T2 thread, also written T-2, has a diameter of 42mm and a thread pitch of 0.75mm. It is also sometimes written as M42x0.75.
The low pitch distinguishes it from other M42 threads.
Omegon
Adaptors 1.25'', 30mm extension tube
$ 24.90
ready for shipping in 24
h
ZWO
Adaptors T2 to 1.25" adapter
$ 42.90
ready for shipping in 24
h
TS Optics
Adaptors T2 to 1.25" adapter
$ 31.90
ready for shipping in 3-7
days