Can you identify this thread?

[sploo]

The attached image is the first item that slots into the focuser on my Skywatcher 300P.

The right side is (unsurprisingly) a smooth tube with a 2" OD.

On the left there's a male thread with an (approx) 42mm OD, approx 0.75mm pitch (i.e. a T thread for a camera adaptor, rather than a 1mm pitch "M42" thread).

The female thread on the left side is something I can't identify. It's approx 35.5mm ID, and looks to have a 1mm pitch. Anyone know what it's for, and what this part is (i.e. I want to buy another, so I can leave one permanently screwed to a camera T adaptor)?

PS I couldn't see anything obvious on https://agenaastro.com/articles/guides/miscellaneous/astronomy-threads-explained.html

[tooth_dr]

The 1.25" eyepiece adapter screws into this.  I have the same focuser arrangement on my 250px.  I don't know the thread side but that is it's purpose.

 

[lenscap]

The female thread is M36 X 1mm.

You can get the adapter plus 1.25" eyepiece holder here;   https://www.rothervalleyoptics.co.uk/skywatcher-2-to-125-adaptor-explorer-models.html

Edited March 6, 2020 by lenscap
added link

[sploo]

Many thanks both. If the only purpose of this thread is for the 1.25" eyepiece adapter then, because it couldn't be used when a DSLR is mounted onto the male T thread, I could buy a 2" eye piece to T thread adaptor for permanent attachment to the camera, and leave this original ring for eye piece use only.

I just wanted to make sure there wasn't some really important photography related reason for having that female thread.