Focuser problem, Skywatcher Dobsonian (the nightmare continues)

[FPM]

Could anyone with this scope tell me if the thread diameter of the collar which holds extension tubes in place is +/- 60mm, as on the attached photos?

[John]

I thought the thread on that drawtube was M54 - 54mm ?

The replacement adapters that First Light Optics sell as suitable for Skywatcher newtonians are M54 threaded:

https://www.firstlightoptics.com/adapters/astro-essentials-2-inch-compression-ring-adapter-for-sky-watcher-newtonians-and-72ed-refractor-m54.html

 

[vlaiv]

I just checked my 8" Skywatcher dob - and it is indeed M54.

However, it seems not to be universal thing:

https://www.cloudynights.com/topic/782264-sky-watcher-2-draw-tubes-thread-size/

mentions M57/M56, and from the images you posted - I'm inclined to declare it M60 on your scope.

Do however be careful when measuring threads - you did ok in above image - you need to measure male thread - and be careful not to have caliper sit in thread groove - but rather measure thread ridges (from ridge to ridge). Due to tolerances - you will measure slightly below nominal major diameter.

If you did it like that - from your image - it simply looks like it is M60 (and do check spacing between threads - you can do that with calipers as well - but it's better if you have thread gauge for that).