might try the connectors that sell at home depot that hold 2 pieces of the metal rods, like dowl rods. they are the ones without threads. they have diff sizes. its slides over and has a set screw inbedded on each size. might work
That's funny. I was thinking about something like that but had no clue where to find it, other than in my Erector Set from when I was a kid. Both the Erector Set and my childhood are LONG GONE! THANKS!