I think it is either 14 or 16awg, I just purchased some 12awg and that is thicker, I also have 18awg leads that I made up which are thinner than all my ready made leads. I find the 18awg leads are just fine for reading volts and resistance being as they are ultra flexible, but for current you certainly need thicker cables so you can choose either 14 or 16, its your choice.