Cup — The bowl-shaped area where your lips vibrate. Deeper cups produce a warmer, darker tone; shallower cups are brighter and help with higher notes.
Throat — The narrowest point of the mouthpiece bore, measured in drill numbers (e.g., #27) or millimeters. It controls airflow resistance and overall feel.
Backbore — The flared tube after the throat leading into the trumpet. It shapes the airflow and influences tone color, intonation, and blowing resistance.

A deeper cup (like Bach 1.5C) gives a richer, warmer, more symphonic tone — ideal for classical and orchestral playing. A shallower cup (like Bach 10.5C) produces a brighter, more piercing sound suited for jazz, commercial, and lead trumpet work. Most players find a medium-depth cup (like Bach 3C or 5C) to be the best all-rounder.

The most common throat size is #27 (3.73mm) — found on Bach 3C, 5C, 7C, and many others. A larger throat (e.g., #24 / 3.96mm on Bach 1.5C) gives a more open, free-blowing feel with more volume potential but requires stronger breath support. A smaller throat (e.g., #28 / 3.66mm) adds resistance, which some players prefer for endurance and control in the upper register.

The Bach 3C has a medium-deep cup, larger diameter (~16.50mm), and #27 throat — offering a fuller, richer tone favored by many professional players. The Bach 7C has a medium-shallow cup, smaller diameter (~16.00mm), and #27 throat — it's the most common beginner mouthpiece, offering easier response and a brighter tone. The 3C requires slightly more developed chops but rewards with a more mature sound.

A tighter backbore increases resistance and focuses the tone — helpful for lead playing and endurance. A more open backbore reduces resistance, allowing freer airflow and a broader, more resonant sound — ideal for orchestral and solo work. Most standard mouthpieces use a moderately open backbore for balanced performance. The backbore works together with the throat to determine overall blowing resistance.

The Bach 7C is the traditional beginner recommendation — it has a manageable cup depth, standard #27 throat, and a comfortable rim diameter. The Yamaha 11B4 and Bach 5C are also excellent beginner options. As you develop, you may want to experiment with slightly larger diameters (like 3C or 1.5C) for a fuller tone. The most important factor is comfort — if it hurts to play, try a different size.

Throat sizes are often given as drill bit numbers (a legacy from machining). Lower numbers = larger holes. Common sizes: #28 = 3.66mm, #27 = 3.73mm (most common), #26 = 3.81mm, #25 = 3.89mm, #24 = 3.96mm. A difference of just 0.07mm (one drill size) is noticeable to experienced players. European brands often list throat size directly in millimeters.

Many players use a medium-depth mouthpiece like the Bach 3C or 5C as a versatile all-rounder for both jazz and classical settings. However, specialized players often own multiple mouthpieces: a deeper cup (1.5C, 1.25C) for orchestral warmth, and a shallower cup (10.5C, Schilke 6A4a) for lead jazz brightness. The mouthpiece is a tool — match it to the sound you want.