As French horn players seem to use the metric system to describe the size of the mouthpieces, we decided to number our line in a metric way. * A unique quality of our standard French horn mouthpiece line is the unique rim contour. There is definition to the inside diameter and yet the roundness of the rim shape allows for easy movement, as well as a high degree of control and flexibility. * We realize that many French horn players feel a personal affinity with a rim that they have played for many years. There is a certain degree of "comfort" in having the same rim on your face.