This is a BEST BRASS 5D French horn mouthpiece. I purchased it new and used it for about a month, but it didn't suit me, so I'm selling it. It has an inner diameter of 17.5mm, a throat diameter of 4.00mm, and a slightly shallow cup. It's an American shank. It's said to be equivalent to an Alexander 8 mouthpiece from other companies. There are some stains on the gold plating, but it doesn't affect its use.