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.

TS Optics
Tilting Collimator T2
RRP:
$ 63.00
Our price:
$ 59.00
ready for shipping in 3-7
days

ZWO
Tilter T2
$ 82.00
ready for shipping in 3-5
weeks

TS Optics
T2 quick-release connector with 360° rotation, length 5.5mm
$ 65.00
ready for shipping in 3-7
days

Baader
Tilter T2
$ 218.00
ready for shipping in 1-2
weeks

DayStar
Interference Eliminator T2
RRP:
$ 324.00
Our price:
$ 303.00
ready for shipping in 3-6
months