Straight copper alloy electrodes with a drill in the center for resistance welding are always the best solution to perform the resistance welded joint of two sheets.
The straight electrodes with the tip in the center allow their internal cooling as defined by the rules defined by the resistance welding, the full part of the electrode should never exceed two centimeters and the inner cooling tube to the welding electrode, must reach one centimeter from the end of the hole and cut to 45°.
The cooling hole on the straight copper alloy electrode and the diameter of the inner cooling tube, must be proportionate to the diameter of the welding electrode and depending on the welding current.
An additional advantage in using the electrode straight with the tip in the center is that you can make the dressing of the tip using a manual pneumatic sharpener ETD-18 equipped with the blade with the suitable profile at the tip of the electrode for resistance welding.