Horn Mouthpiece YAMAHA 30GP Custom Model: CUSTOM 30-GP Finish: Silver-plated, Gold-plated inner rim Cup: Double cup Inner cup diameter: 17.08mm Bore size: 4.40mm Rim thickness: 3.66mm I purchased this about six months ago, but it didn't suit me, so I'm selling it. Although the inner diameter is small, the double cup allows for good sound in both the high and low ranges. I think the bore is relatively large for this inner diameter. There are lacquer burn marks on the surface, but they do not affect the performance. Please feel free to ask for additional photos or to request a price reduction.