A commonly available, inexpensive 190mm f1:3.8 guidescope comes with no provision for focusing other than screwing in and out the objective lens or sliding the guide camera in and out of the 1.25" eyepiece hole. I wasn't able to focus without an annoying 5mm extension and even then it was sketchy at best. A deluxe version of this guidescope is available but so also is aftermarket helical focusers "for guidescopes". The two do not connect without some special adapter that nobody sells.
The ID of the guidescope tube is a very awkward 50.5 - 51mm x0.75mm thread and the focuser will only screw in to a M36x1mm thread. I found a specific offset that allows full focus range of about 15ft to infinite (and beyond). The adapter flange is slotted to help with installation or removal. After at least 6 revisions, it fits and works well.
240c at 30mm/s, print flat side down. Threads print flawlessly!