Stem Inserts

Stem inserts are thin slices of material glued at the end of the mouthpiece where it meets the shank. They serve no structural function; they insert a thin band of color where the mouthpiece and shank meet, making the joint line visible.

The usual arrangement consists of a somewhat thicker cap piece that sits directly against the face of the shank, with one or more thin slices behind it. The whole stack is threaded onto the pin that connects the mouthpiece to the shank and bonded into a single body with the mouthpiece using epoxy.

Insert Material

Ebonite, acrylic, horn, and hardwoods are used for the slices. The choice is not determined by color harmony alone; how the materials change over the years is also taken into account. Ebonite, the classic mouthpiece material, is a hard rubber obtained by long vulcanization of natural rubber, and the sulfur content in its composition can range from 25% to 80% by weight. Ultraviolet light oxidizes this surface; free sulfur exposed to moisture converts to sulfates and sulfuric acid, and the surface shifts first to a grayish green, then to brown. So the initial color contrast should not be assumed permanent. A detailed comparison of materials can be found in the mouthpiece materials entry.