This is a holder/handle for the spotweld electrodes of a battery spotwelder. Specifically the ones found on Aliexpress. With this Thing you can hond both electrodes with one hand.
You can make your own spotwelder using a microwave transformer.
Some things you'll need:

• Spot welding electrodes
• Spot welding timing and current control
• 9V AC transformer
• Spot weld pens

This model is made by Eric van der Aar, and is licensed under CC BY 4.0.