Rather than have two large tripods for a Meade 8" SCT telescope and Skywatcher NEQ-6, I went looking, unsuccessfully, for an M12-1/2" UNC cross-over (Skywatcher to Meade). For those with a lathe, turning one up would work, but lacking that, I opted for a welded solution.
I bought a 1 x 1.5" UNC bolt (Speciality Fasteners, Canberra) and an M12 coupler (Bunnings). An M12 bolt would also work, but I wanted plenty of thread. I cut the extender in half, and a friend TIG-welded the parts together.
To spread the load from the smaller diameter Skywatcher tripod (130mm) to the base of the Meade (165mm), I used a piece of 17mm formply with a 1/2" hole, 225 square (I plan to round off the corners). An aluminium plate would also work.
Thanks to Garry for the welding.