JK Mouthpiece Naming System
JK is one of the few brass brands that behaves like a real taxonomy instead of a historical pile-up of arbitrary numbers. The logic is consistent: diameter families, depth letters, bore progression, shank options, and instrument-specific branches like Exclusive, USA-Line, K/M horn, and Apple vs Classic tuba.
A manufacturer that actually tells you how the system works
The most important JK idea is that the model code is supposed to be legible. In the Exclusive line, lower numbers generally mean larger diameters, letters nearer the start of the alphabet mean deeper cups, and each family keeps its own internal logic instead of borrowing a vague Bach-style shorthand. That makes JK unusually useful for players who want to move between trumpet, cornet, flugelhorn, horn, trombone, euphonium, and tuba without guessing.
The 1–10 trumpet ladder is the cleanest place to start
JK trumpet logic revolves around the Exclusive series. Numbers move from larger to smaller diameters, while depth letters move from deeper to shallower. The standard trumpet line is built around a 3.7 mm bore, with Classic, Big Band, and Piccolo branches altering the bore and cup strategy while keeping the rim interface intelligible.
| Range | Meaning | Depth Logic | Practical Reading |
|---|---|---|---|
| 1–3 | Largest trumpet diameters | A–F | Symphonic or broad-sounding players; closest to Bach 1 / 1¼ territory |
| 4–5 | Core professional range | A–G | The most useful JK trumpet sizes; size 5 sits closest to the modern 3C lane |
| 6–7 | Medium-small | A–G | Common crossover sizes for players coming from Bach 5C or 7C territory |
| 8–10 | Smallest diameters | A–G | Efficiency-first options and smaller embouchure fits |
K vs M is one of the clearest tonal forks in the brass world
JK horn players are really choosing between two tonal philosophies before they ever choose a size number. K-series mouthpieces favor funnel-cup depth and a darker German profile. M-series mouthpieces favor a bowl-cup response with more upper-harmonic clarity and a flatter rim feel. The size and depth letters then fine-tune resistance and embouchure interface within that family.
| Family | Cup Logic | What It Means |
|---|---|---|
| K Series | Funnel cup | Rounded rim feel and dark German timbre |
| M Series | Bowl cup | Brighter overtone profile with a flatter, more stable rim |
| Stefan Dohr | 2EM SD / related signatures | Elite orchestral collaboration around the M-series logic |
| Ralph Ficker | RF models | Oversized-diameter variants for players who need more rim real estate |
P, PO, Apple, Classic, and the importance of shank fit
JK low brass makes more sense once you stop expecting a single universal ladder. Trombone uses P for the main tenor family and PO for the larger bass trombone range. Euphonium and tenor horn build from the same sizing discipline but require shank attention. Tuba splits into Apple and Classic tonal families, with the AA suffix extending depth beyond the usual A–E range.
| Code | Meaning | Why It Matters |
|---|---|---|
| P | Standard tenor / alto trombone range | The main tenor-family numbering |
| PO | Largest bass trombone diameters | Purpose-built bass trombone sizes |
| PS | Specialty / artist models | Includes the Cieslik-type specialist designs |
| Tuba Apple | Bowl-style tuba family | Traditional broad German cushion of sound |
| Tuba Classic | Conical tuba family | More centered attack with less internal congestion |