[glend (Glen)]

Alex, I have resorted, in the past, to using Anti-seize compound, which is sold to use on engine and auto parts ( a good example is on lug nut threads). Anti-seize works, I still have a stick of it, in a push up tube, like the kids old push pops. However, while it works well, it will leave traces of the grey paste (zinc i believe) on the threads of both parts joined, and can drop traces on other parts during assembly and disassembly. It is difficult to clean off when down inside threads.
My secret method (preferred), is to use duct tape, wrapped around the two parts (in opposite directions) with a tail remaining to become the sticky handle to give you purchase in rotation. The tape adhesive helps your fingers maintain a grip on the two sections when you rotate them (especially if you take a wrap of the tape around a finger as a lock). I have used this for many years, it is fast, and clean, leaving no residue. My current preferred tape for astro threads is the 3M Blue masking type tape, which is easily removed but has good shear strength when pulled laterally during rotation.

Another technique that can work well is to put on some tight fitting latex gloves, the usual ones work ok, but wash the lubicrating powder off the outside of the gloves once you put them on. They should feel slightly sticky on the tube extensions, when grasped. Just squeeze the two locked sections and rotate, most of the time this can work.