Choosing the correct tungsten electrode size depends on the specific welding application and the type of welder being used. Here are some general guidelines for selecting tungsten electrode size:

1. Diameter: The diameter of the tungsten electrode should be selected according to the welding current and the thickness of the material to be welded. Smaller diameter electrodes are suitable for lower current levels and thinner materials, while larger diameter electrodes are suitable for higher current levels and thicker materials.

2. Length: The length of the tungsten electrode should be selected based on the specific welding machine and welding gun used. Different welding gun designs and welding machines may require different electrode lengths to ensure proper fit and performance.

3. Current type: For AC welding, pure tungsten electrodes or electrodes with rare earth additives such as cerium are typically used. For DC welding, thoriated tungsten electrodes are typically used. The size of the electrode should be selected based on the specific requirements of the welding process and the type of current used.

Be sure to consult your welder manual and consider specific welding parameters and material thickness to determine the appropriate tungsten electrode size for a given application. Additionally, consulting a welding professional or expert can provide valuable insight into selecting the appropriate tungsten electrode size for a specific welding task.