From the campaign:
Tinker Gearchips are a series of metal gaming coins, made of a zinc alloy and plated with a variety of metal finishes. They are standard poker chip sized, 39mm in diameter and 3.5mm in depth, and they weigh just under an ounce each. They are solid coins, with a good heft to them. The Tinker logo features on one side, and the Project Khopesh logo on the other (we're not really sure which one is "heads" and which is "tails"). Their gear-toothed edges let them mesh with each other, because hey, if you're making gear coins, they should work, right?