Thin Metal Tip
Eastwood Automotive has a great set of adapters for your AC stick welder.
The diode reduction with special electrodes allows sheet metal welding (automotive) with a lot better penetration / beads than a wire. Especially when fabricating custom like some lap welds.
Copper backer a must to control burn through.
The spot welder adapter doesn't require pilot holes, and reduces heat distortion when stitching.