This is the new style Duo. The mouthpiece is around 16mm in thickness. The orignal Duo was a lot thicker and was able to be used either way up, as one side of the bit was a straight bar and the other side had an indent for more tongue room. With this style been a lot thinner the option of tongue relief is minimal. We did ask Sprenger when they were over here in England a couple of years ago about the thickness of these bits and were the original bits still available to order, and unfortunatly the answer is no. However if you look on the non dressage legal there is a version made by Happy Mouth which is similar to the old style Duo.