Crescent moon labret. 1.2mm (16G) surgical steel 316L internally threaded bar with a flat back.  The bar is 6mm long, the moon is about 5mm long and the back is 4mm diameter.

Flat backs (Labrets) are suitable for a variety of piercings. Lips, Tragus, Helix, Lobe etc Internally threaded labrets are better than externally threaded as there is no thread to catch on the piercing as you insert it. 

1.2mm x 6mm