This thing clamps onto a microphone stand and holds a device with a standard tripod socket. One picture shows its intended use - putting a Zoom H2 audio recorder on a stand below the microphone.
Features a pressure plate to clamp the microphone stand so that the stand is not marred by the screw.
The SCAD file is somewhat parametric so it should be trivial to make this clamp onto tubes of different diameters. Also, the SCAD script builds the stand clamp and the tripod head separately so it would be easy to use the clamp separately as a part of other things.