The size of the electrode, and the depth it is inserted into the water both effect current density. The larger the electrode size and the further it is put into the water both give a larger electrode area. The larger the electrode area the lower the current density and the smaller the particles of silver will be. Smaller silver particles are better.
10 ga wire has a diameter of 0.1", 12 ga has a diameter of 0.08", and 14 ga has a diameter of 0.06". If we have 4" of depth into the water the 10 ga wire would have an area of about 2.5" both electrodes added together, the 12 ga wire would have an area of about 2.0", and the 14 ga wire would have an area of about 1.5".
Using voltage and current controls you can adjust the current density to accommodate the various sizes, but if you don't have those you would probably just be better off to use a larger size. However at lower voltages with a current limiter (the addition of a current limiter in your set up is highly recommended), it may take a very long time to brew a batch.
A couple of things to keep in mind... The lower the current density the longer the brew time will be. Also, the lower the current density the longer the electrodes will last before being consumed.
I am not aware of a formula that gives you particle size as a function of current density, but I think there has been enough trial and error testing done that while this may not be formally known it most likely is factored into the design of the various units.
The electrodes that I use have an area of about 4.21". They are strips that are 0.25" wide by 0.013" thick.
If you are using 36 volts you should be able to use the 10 ga wire without problems. I believe my unit runs at a voltage near that and I don't have any problems. If you look at the way the silver puppy is set up you will see that the electrode is wire but instead of a straight drop into the water it is in the shape of a U. This doubles the surface area, so you can adjust things by simply playing with the electrode design.