Pilot tube ferrules

The pilot tube on my Weil McClain gas boiler is completely corroded, to the point where it was in two pieces. Not sure what happened, since the unit was serviced ~1 year ago, but anyway…

It seemed like straightforward and safe enough DIY repair, but I’m stuck on a step that shouldn’t be difficult.

I purchased this kit: https://wal-rich.com/product/1-4-x-1-8-x-36-pilot-tubing-kit/ It looks basically identical to the existing hardware, and seems to thread just fine into my gas valve and pilot nozzle.

If I understand it correctly, you poke the tube all the way down in the fitting, thread it in to where it goes, snug it down and the ferrule should crimp onto the tube and snap off of the nut.

I have been tightening down the fitting with increasingly unreasonable amounts of force, and no matter what I do, the ferrule never crimps on and the tube can be easily pulled out with a gentle tug.

The hardware came with the tube, so it damn well better be the right size. What am I doing wrong? Am I just a moron? I didn’t expect to be ground to a halt by something so simple.