What diameter wire do you use?

Generally speaking, the standard wire used in most EDM jobs is .010" in diameter. This is an optimal size that has enough surface area to conduct sufficient current to yield enough speed, yet not so much surface area as to increase the raw material wire and filtration cost. From here, most alternative wire diameter sizes involve smaller wire diameters that have smaller kerfs (or the minimal material that is removed in a cut), and smaller internal radiuses.
The other wire sizes we use besides .010" is: .013", .008", .006" ,and .004".
The minimal internal radius in a part depends on the type of cut being performed. With finish cuts, the .010" diameter wire may leave a .0058 wire radius in the part.
With a few exceptions, the smaller the wire, the longer the time to cut and the more the cost.