There might not seem to be much of a difference between the types of body jewelry that exist out there, but really, there are two majorly different types that someone with a new piercing especially might wish to pay attention to. These would be the externally threaded and the internally threaded screw in jewelry types. The externally threaded jewelry type is one that would have the screw-looking part so that the wearer can screw on the little ball if he or she is wearing a barbell. This is what most screw-on tunnels would likely have.
While this is the more common type of screw-on jewelry, and most people wear it whenever they please, this might be because their piercings have already healed very well and don’t get irritated easily. However, if your piercing is still not fully healed, it may become raw from the rough movement that inserting this kind of screw-like shape would bring on. After all, inserting one is pretty much like shoving an actual real life screw through your piercing- and if the skin is still sensitive, it will not respond very well.
So if you have a mature, fully healed piercing, you can go ahead and stick to the familiar externally threaded jewelry type. But if you find that those really become bothersome with a still delicate recent piercing, then you might be better off trying a slightly different solution. An internally threaded screw piece would have the screw bit on the inside, thus making it much smoother and easier to insert into your piercing. Once your piercing has completed its healing process and is no longer so vulnerable, you can easily return to using the more common externally threaded jewelry pieces.