I have cotton cargo pants (from Old Navy, I think) where the outside seam has two topstitches and the inside seam only has one. Even the seam between the left/right halves has a topstitch.

How is that possible? What tool or technique was used to get a topstitch on every major seam?

The only thing I can imagine is a sewing machine where the needle sews parallel to a long, thin base, allowing each pant leg to be topstitched after being joined with a stitch when they were inside out.

Here are pictures of the stitches for a single leg of my pants. Note how one is double topstitched, and the other is single. The point is that all stitches on the pants are like this (with no breaks), so I don't see how they did it unless they have a special machine.

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