The Mares Jax Mouthpiece has been designed to be a custom fit mouthpiece. This was created as every mouth bite is different and not everyone is comfortable with the standard silicone mouthpiece that comes on a regulator when purchased. The Jax allows you to mould it to fit your mouth and teeth to fit you perfectly. You simply immerse the Jax in boiling water for a few seconds, pop it in your mouth and bite down on it for a personalized mouthpiece. What happens is the silicone will mould to you exact bite making it super comfortable. When you take it out you will be amazed. Jax can be fitted on all or any Mares regulators. A reason that the Jax is so popular is because many divers get jaw fatigue when is not correct, so the new Mares Jax mouth piece is perfect as it can be custom fit to you. It is easily attached by a small zip tie, so if you upgrade for change you gear, you can take your mouthpiece with you. EASY!