This is a rig for testing the Pololu Quadrature Encoder and related components. When you're working out the software for a robot, having the wheels off the ground in a stable rig makes life easier, particularly if you're testing your circuitry on a breadboard, like this one from Adafruit:
Information about the encoder can be found here:
This setup uses 8 machine Phillips pan head screws sized #2 -56 x 1/4". I order mine from here:
Check the photos for assembly instructions. If something lacks, lemme know.