Thank you for viewing. This is a Willie's PJ AX. It has an inner diameter of 17.53mm, a throat diameter of 4.2mm, a U-cup, and an Alex shank. I used it a few times after trying it out, but ended up going back to my usual mouthpiece, so I'm selling it. As stated on DAC's website, I think it's a mouthpiece that's easy to play on thanks to its exquisite rim shape. If you're interested in Willie's, which is currently popular among professional players, please consider it. There are some small black spots, but they will probably disappear if you polish it.