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.
Baader
90°, T2 star diagonal with 35mm of free aperture
$ 281.00
ready for shipping in 1-2
weeks
Baader
Zenith prism T-2/90° 32mm prism
$ 128.00
ready for shipping in 1-2
weeks
TS Optics
Diagonal prism T2 90°
$ 103.00
ready for shipping in 3-7
days