What adapter is this?

[bojan]

The thread at lower side (male, at "Lock" ring) is standard T2 (M42 x 0.75 mm).
Upper one (female) is ~ M35 x 0.75 mm.
Anyone knows where this adapter is used?

[Dennis]

According to the following:

Could this be for:
ETX/NexStar/NX4Threads (1.375"-24)
Meade's ETX telescopes with apertures from 90mm to 125mm,
Celestron Nexstar 4SE telescope,
Some relatively newer Celestron C90 spotting scopes, and a few other small Maksutov-Cassegrain telescopes.

https://agenaastro.com/articles/guides/miscellaneous/astronomy-threads-explained.html#etx

Cheers

Dennis