What is the coloured thread in the waistline of your pantyhose?

Is it there by mistake? This is highly unlikely since factories are stocked with plenty of threads and stitching is done automatically.

No, it’s there on purpose, it’s actually a size indicator. Red, blue, yellow… it tells the factory what size that hosiery pair is before it is packaged. This feature helps with quality control too.

coloured size indicator thread in pantyhose

This is a red thread on a pair of fleece lined leggings by Gabriella.