I have one of the mag-base holders with ball joints at the top and at the base. It is locked into position by a single knob at the central joint. I took it apart a couple of years ago (after much cursing and swearing over not being able to figure out how it came apart), after which I though 'huh, how simple, I won't forget that'. No prize for guessing why I'm writing this now - and this time the cursing and swearing hasn't worked!
Does anyone remember how these damn things come apart?