This labret is not equipped with either an external or an internal thread - it's threadless. It features a small pin on which the stone is attached. As you can see in the picture above, the pin is slightly curved, which enables you to snap it into the labret bar. To open it, pull out the pin and to close it, push it into the shaft. The threadless pin will be secured and won't fall out. 

The labret is available in several lengths and in the two stone colors that you can see in the pictures. When you choose the length of the labret, you must also select the size of the stone from three options. 

The entire piece is made of surgical steel, except for the stone, of course. The opal is not genuine, as real opals are not suitable for jewelry use. It's a synthetic opal, but very similar to a real one.