Nylon thread, also called monofilament thread or invisible nylon, is a thread that has a single filament. It looks similar to the fishing line because some fishing lines are also made of nylon. Nylon thread and fishing line are essentially the same thing but have different thicknesses. While nylon thread has a thread size of 0.012 inches as the maximum thickness, the fishing line has a thread size starting from 0.013. With nylon thread, you get to choose from a wider range of thread sizes, depending on your sewing needs. Monofilament threads are transparent and are mostly used in sewing athletic wear and for sewing labels on clothing when it is difficult to find thread colors matching the fabric or label. Nylon thread is versatile because of its lack of color, but one of its drawbacks is that it can be a bit scratchy and irritating when it comes in contact with the skin. On the other hand, nylon is just one of the common materials used to making fishing lines. They are sometimes made with silk or wire. A fishing line is not an ideal thread material for sewing because it is very strong and thicker than normal threads, which can cause the fabric to tear or break.