Internally threaded jewellery
Internally threaded jewellery is top of the range. This is the best type of jewellery but also the most expensive. It can be more comfortable to put in and there's no risk of the thread catching the piercing.
Internally threaded jewellery and accessories aren't as interchangeable as externally threaded jewellery (where only the gauge needs to be the same).
Due to slight differences in the threads the thread types need to match as well as the gauges. To make this simpler we've named these type A, B, C and D. So for example a type A accessory will fit a type A post, but a type A and B will not fit together even if they are both the same gauge.