5MM Backbore Size Reference: Trumpet, Cornet, Flugelhorn, Custom

The 5MM Backbore is an extension of the Throat that determines tonal color, intonation and projection pattern. 5MM Backbores are available in over 100 size variations.
* Extended length backbores available to adjust gap (call to order)

Most standard mouthpieces have backbore measurements in the following range:
Beginning Diameter = .20 to .22 inches
End Diameter = .31 to .35 inches

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

Need help with sizes and options? Call us at 303.657.2747 or email harrelsontrumpets@gmail.com to discuss your needs with our team of experts.


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) Test any 5MM variations in our shop to find the perfect setup
Understanding Size options
Beginning Diameter - First 2 digits, dimension of the ID top in hundredths of an inch, must match Throat end diameter
End Diameter - Second 2 digits, measured at the very bottom diameter