This is a Hotwheels C-Clamp with track connectors added on it.

I'd like to thank ADN_NMX for designing his connector.
http://www.thingiverse.com/thing:755400
This was the other part used with the clamp to allow for the track to connect.

NOTE: I did not modify the long screw intentionally. it will leave a gap.

clamp opening with screw opened up is 67.2mm
clamp opening with screw closed inward is 28.8mm

if you are going to need a smaller opening when the clamp is tightened you will have to elongate the screw.