Removing Anodized coating. The product is “Whinks” Rust Stain remover
Most food chains carry it. I bought mine a local hardware store had a few fittings and an Edelbrock fuel filter. It took a little over eight minutes to remove the finish. For large pieces maybe you could brush it on. I started with oven off didn’t do the job.

My neighbor said it probably wasn’t anodized but paint. It was an Edlebrock fuel filter & fuel pressure gauge fitting.