5MM Backbore Size Reference: Trumpet, Cornet, Flugelhorn

The 5MM Backbore is an extension of the Throat that determines tonal color, intonation and projection pattern. 5MM Backbores are available in 35 size variations in the standard straight taper or custom shapes (special order).

Most standard mouthpieces have backbore measurements in the following range:
Top ID = .20 to .22 inches
Bottom ID (end of mouthpiece) = .31 to .36 inches

A 3C backbore is typically .21 by .32-33 inches and is designated as 21.33 as in the example illustration.

Need help with sizes and options? We're here to help. Call us at 651.330.7774 or email harrelsontrumpets@gmail.com to discuss your needs with Jason or Christine.


Getting Started
The easiest way to get started in the 5MM System is to choose a Rim close to your current mouthpiece. To save you time and energy, you may order your 5MM by simply telling us which brand and size options you prefer and we will do all the cross reference work to get your mouthpiece built right the first time. It is not necessary to learn our sizing system.

1) Order based on your current size
2) Build your own size
3) Experiment with a full kit
Understanding Size options

HT Size - this 4-digit number designates the top and bottom diameters, a letter designates the shape
ID Top - First 2 digits, dimension of the ID top in hundredths of an inch, must match Throat end diameter
ID Bottom - Second 2 digits, measured at the very bottom diameter
Shape - standard is a straight taper, other shapes available as special order only
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