Gears are needed to craft Buildcraft Engines and machines, like the Quarry. The gears must be constructed sequentially, so in order to make one Diamond Gear you need four sticks, four cobblestone, four iron, four gold and four diamonds.
Note: The recipe below is for the Assembly Table, which currently has no Template on the wiki. The Assembly Table requires energy in the form of buildcraft MJ (minecraft joules) to work. IMPORTANT: The recipe calls for two Diamond Tranport Pipes, which cannot be shown properly in the Template below.