Like others I have had problems to reach the short 55 mm distance between the reducer and the sensor (there was a thread here but I don't find it anymore). I solved it by widening a standard Pentax-K/T2 adapter with a metal lathe and screwing in an M48 threaded adapter ring.


There possibly is a better solution: Teleskop-Express: TS-Optics ultrashort Adapter from T2 (M42x0,75) to Pentax and Sigma DSLR Bayonet


With that adapter they say you only loose 1 mm (instead of 14 mm or so with a standard Pentax/T2 adapter) to go on with a female T2 thread. For going on with M48 (2") on the telescope side this adapter (male T2/female M48) can be added: Teleskop-Express: TS-Optics Adapter von M48x0,75 auf T2 - kurzbauend. This would add another 3.5 mm to the optical path (4.5 mm total).


Besides the possibility to connect focusers with short sensor distances this solution may offer possibilties to use additional stuff like OAG, filter drawer, filter wheel etc. and stay within the recommended distances.


Important: You should inform yourself directly at the distibutor before buying in case I have made mistakes.


Cheers
Pete

That looks like a solution that will allow a thin OAG for my Meade LX850 ACF 12" and my 8RC

I ended up doing the exact some thing.


I also made another one taking a stock M42 to PK adapter, and loosened the set screws and completely removed the inner M42 component. I then took a plain 2" barrel and substituted it where the M42 component used to be and tightened the set screws back down on it.

Great idea. Where does one get plain 2" barrels?

I guess this was the thread Peter: Where to get 48mm Pentax T-ring? - PentaxForums.com

So a lathe would come in handy.

It is possible to use standard M48 adjustment rings. But they are quite thin and the threads are mostly quite short. They tend to show some deformation when the set screws alone are used to fix them. I have tinkered one adapter with this type of connection but secured it additionally with super glue. But because of the short M48 thread and the long thread of the reducer I do not reach 55 mm with that solution.

Baader Planetarium has some „wide“ adapters for Canon, Nikon and Sony with M48 connection but not for Pentax. The reduction piece is very sturdy and can be used in a standard Pentax K/ T2 adapter that is widened with a metal lathe to 52 mm. This is what I finally used and it is great:
Reducing piece S52 / M48
The dovetail on the outside fixes the whole thing very good together with the set screws. And the screws can be used to rotate the camera for framing purposes after it is attached to the scope.

That sounds like a different solution than the one I was replying to, which depends on the inside diameter of the outer portion of an M42-to-PK T-ring being the same (just a little less, actually) as the outside diameter of a 2-inch eyepiece barrel. This may not be true for all M42-to-PK T-rings, I don't know (depends on that dimension being part of the M42 T-system standard, which I'm not sure is the case). If the barrel in question is aluminum and not chromed steel, then the three tiny setscrews should actually grip the barrel quite strongly.

Coincidentally, that is actually how the Lumicon 2-inch Newtonian Easyguider (an OAG) I have works. To adapt it for different cameras all I need to do is remove the inner part of the T-ring for the camera in question and fasten the outer part over the adjustable flange that is part of the Easyguider. I discovered this myself. Lumicon (long out of business now) maintained that you had to specify your camera when you ordered the device from them. Quite evidently, that's all that they did at the "factory" before sending one out to the customer. I remember arguing with someone long ago on sci.astro.amateur who refused to believe it.

P.S. sci.astro.amateur still exists as a Google group but IMO it is as useless as it ever was for the last ten or so years.

I just created my own PK- M48 adapter by removing the T2-PK dovetail ring and inserting an M42-M48 adapter into the PK part of the T2-PK adapter.
It fits ok, I just have to make three marks with a drill to ensure nothing falls apart.
But then I figured, there must be an adapter piece that somehow fits into the ø52mm PK part of the T2-PK adapter (after all, this is 'the' world of adapters). I hadn't seen your reply mentioning the Baader M48-S52 ring Peter. I found it as well, it turns out it's a perfect fit for my TS Optics PK-T2 adapter - fantastic!!!
Had I only known that the number of adapters in the fantastic world of Astrophotography matches the number of stars in the universe...

Teleskop-Express: TS Optics T2 Ring f

Teleskop-Express: Baader M48 Filtergewinde Umkehrring mit S52 Schwalbenschwanz