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
T2 adapter ring, 7mm (female/female)
$ 34.90
ready for shipping in 24
h
TS Optics
1.25" Filter Holder for T2-threads
$ 37.90
ready for shipping in 24
h