most common dual-bore combinations are , , , , for tenor trombones, and for bass trombones. Mouthpiece The mouthpiece is a separate part of the trombone and can be interchanged between similarly sized trombones from different manufacturers. Available mouthpieces for trombone (as with all brass instruments) vary in material composition, length, diameter, rim shape, cup depth, throat entrance, venturi aperture, venturi profile, outside design and other factors. Variations in mouthpiece construction affect the individual player's ability to make a lip seal and produce a reliable tone, the timbre of that tone, its volume, the instrument's intonation tendencies, the player's subjective level of comfort, and the instrument's playability in a given pitch range. Mouthpiece selection is a highly personal decision. Thus, a symphonic trombonist might prefer a mouthpiece with a deeper cup and sharper inner rim shape in order to produce a rich symphonic tone quality, while a jazz trombonist might choose a shallower cup for brighter tone and easier production of higher notes. Further, for certain compositions, these choices between two such performers could easily be reversed. Some mouthpiece makers now offer mouthpieces that feature removable rims, cups, and shanks allowing players to further customize and adjust their mouthpieces to their preference. Plastic Instruments made mostly from plastic, including the pBone and the Tromba plastic trombone, emerged in the 2010s as a cheaper and more robust alternative to brass. Plastic instruments could come in almost any colour but the sound plastic instruments produce is different from that of brass. While originally seen as a gimmick, these plastic models have found increasing popularity of the last decade and are now viewed as practice tools that make for more convenient travel as well as a cheaper option for beginning players not wishing to invest so much money in a trombone right away. Manufacturers now produce large-bore models with triggers as well as smaller alto models. Regional variations Germany and Austria German trombones have been built in a wide variety of bore and bell sizes. The traditional German Konzertposaune can differ substantially from American designs in many aspects. The mouthpiece is typically rather small and is placed into a slide section with a very long leadpipe of at least . The whole instrument is typically made of gold brass. They are constructed using very thin metal (especially in the bell section), and many have a metal ring called a kranz ("crown") on the