External threading is a jewelry threading in which the bar of the jewelry has a threaded rod. This is the opposite of the internal threading, in which the bead is the one with the threaded rod. It is an important distinction all piercing enthusiasts need to know about. Threaded jewelry, such as barbells, can be either internally or externally threaded. Jewelry with internal threading is generally considered better because the bar is smooth so it doesn’t hurt the piercing or fistula when you insert the jewelry. On the other hand, jewelry pieces with external threading have a bar with a threaded rod that you need to insert through the piercing. The threaded rod might snag on the tissue and hurt the fistula. This can injure your piercing. It is particularly a problem for new piercings in healing. This is why those with new piercings should avoid external threading or be very careful with externally threaded jewelry.
Generally speaking, jewelry with external threading is seen as less safe and inferior to internally threaded jewelry, though it doesn’t mean that externally threaded jewelry is always bad. For example, jewelry with external threading might be okay for short-term wear, but only if your piercing is old and well-established. You should never use it for new piercings in healing. Also, external threading might be okay for very small gauges because it is very difficult to make in internal threading.