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.
ASToptics
Nikon lens to 1.25"/T2 adapter
$ 93.00
ready for shipping in 24
h
ASToptics
M42 FILTER SLIDER SYSTEM (1.25") + TRIPOD INTERFACE
$ 218.00
ready for shipping in 3-5
weeks