Bach Backbore and Throat Specifications

Key to Backbore Specifications

Except in general terms, identifying backbores by size isn’t possible, because they also vary in shape. Various combinations of size and shape darken or brighten the tone, raise or lower the pitch in one or more registers, increase or decrease volume. In each instance the effect depends in part on the throat and cup used with the backbore.

Trumpet and Cornet

Standard: Models without letters: 10 backbore
"A" Cup Models: 24 backbore
"B" Cup Models: 7 backbore
"C" Cup Models: 10 backbore
"D" Cup Models: 76 backbore
"E" Cup Models: 117 backbore
"F" Cup Models: 76 backbore
"V" Cup Models: 25 backbore
 
Special: No. 24: bigger, darker, symphonic
No. 7: dark, Schmitt style
No. 3: dark
No. 117: favors the upper register, standard piccolo trumpet backbore
No. 87: big, free blowing
No. 76: bright edgy sound; helps upper register
No. 41: bright, more resistant
No. 57: lively, helps raise pitch on some notes, good high register.

Flugelhorn

Standard: No. 112
Special: No. 119: more resistance, brighter

Horn

Standard: No. 602
 
Special: No. 614: free highs
No. 613: big, open

Tenor Trombone (small shank)

Standard: No. 402: most models
No. 413: 61/2AM
No. 420: 61/2AL- 5GS
 
Special: No. 402: standard
No. 413: symphonic
No. 420: dark, euphonium
No. 411: warm, lyric tone

Bass Trombone/Large Shank Trombone

Standard: No. 429
No. 800S: 1G, 1-1/4GM ,1-1/2GM
No. 413: 6-1/2AM
No. 420: 6-1/2AL, 5GS
 
Special: No. 429: standard
No. 428: slightly larger, darker
No. 800S: larger, darker, more free blowing
No. 420: dark, euphonium/tenor backbore
No. 413: symphonic tenor backbore

Note: Numbers are factory part numbers for tools.

Key To Bach Throat Sizes

Numbers and letters are drill bit sizes. The smaller the number, the larger the throat. Generally, larger throats make freer-blowing mouthpieces with more volume possible. However, as the throat size increases, the upper register tends to sharpen; the player may tire more quickly.

Trumpet and Cornet

Special: No. 28, 3.57mm/.141"
Standard: No. 27, 3.66mm/.144"
Special: No. 26, 3.73mm/.147" (Standard Mega Tone)
No. 25, 3.81mm/.150"
No. 24,3.86mm/.152"
No. 22,3.99mm/.157"
No. 21, 4.04mm/. 159"
No. 20,4.09mm/.161"

Flugelhorn

Standard: No. 22, 3.99mm/.157"
Special: No. 21, 4.04mm/.159" (Standard Mega Tone)

Horn

Standard: No. 16, 4.50mm/.177"

Tenor Trombone (small shank)

Standard: 5.85mm/.230"
Special: 5.94mm/.234" (Standard Mega Tone)
E, 6.35mm/.250"
F, 6.53mm/.257" (symphonic) (Standard 6-1/2AM)
G, 6.63mm/.261" (euphonium or large tenor) (Standard 6-1/2AL & 5GS)
17/64", 6.73mm/.265" (Standard Mega Tone 6-1/2AL & 5GS)

Bass Trombone/Large Shank Trombone

Standard: 7.00mm/.276"
Special: J, 7.04mm/.277"
7.53mm/.296" (Standard 1-1/4GM & 1-1/2GM)
N, 7.67mm/.302"
8.1Omm/.319" (Model 1G)
F, 6.53mm/.257" (Standard 6-1/2AM)
G, 6.63mm/.261 " (Standard 6-1/2AL & 5GS)
17/64", 6.73mm/.265" (Standard Mega Tone 6-12AL & 5GS)

Tuba

Standard: 8.33mm/.328"
Special: S, 8.84mm/.348" (Standard 24W, 24AW, 7 & 18)
9.00mm/.354" (Standard Mega Tone 7, 18 & 24AW)
R, 8.62mm/.339" (Standard Mega Tone 12 & 22)