Thank you for viewing. This is a tool for repairing dents in the shank end of a mouthpiece. Insert it into the shank end and gently tap with a wooden mallet to correct and repair. It supports from horn to tuba. The thick part is 12.3mm, and the thin part is 5.5mm. This tool is specifically designed for mouthpieces, with careful consideration given to the angle, etc. There may be scratches from the manufacturing process. The mouthpiece in the image is not included. Please purchase without commenting. Please refrain from comments asking for a price reduction. If you are interested in used or new mouthpieces, please search for "Net Brass".