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Flex Coupler

From: $25.00

Flex Couplers come in half sizes from #2 through #7. Each half size changes the gap by 1/32″ (thus a full size changes the gap by 1/16″).

The smaller the Coupler number, the larger the gap. Flex Couplers use the same shank sizing as Reeves sleeves as this is the industry standard for shank sizes.

If you’re unsure of where to start, we recommend you buy one each of the most commonly used Flex Couplers (4.0, 4.5, and 5.0) as a great way to get started.

Flex Couplers will only work on mouthpieces that have been converted for use with
Flex Couplers or Reeves Sleeves.

Detailed Gap information

SKU: N/A Category:


Receiver cut-away showing the "gap"

Receiver cut-away showing the "gap"

The Annulus, or "Gap" as it is commonly referred to, is the space (chamber) between the end of a trumpet mouthpiece and the beginning of the leadpipe.


  • Make the upper register as easy as possible.
  • Improve your endurance.
  • Give you a full, resonant sound full of harmonics, or tonal colors.
  • Improve the low register.
  • Ensure the best intonation possible with your mouthpiece, your trumpet, and the way you play.
  • Give you more sound for less work.
The "gap" affects the pitch center, or slot of every note on the trumpet.
It does this by affecting the intonation of every note.

When the gap is not correct, you must compensate using your chops and air in an effort to make all the notes be in tune and sound as even in possible. This means you are working harder than you need to to play the instrument.

Signs of an incorrect gap:

  • Some notes are sharp and some notes are flat.
  • The upper register speaks well, while the low register speaks badly.
  • The low register speaks well, while the upper register is difficult.
  • All or some registers feel stuffy.
  • All or some registers feel too open.
The video below explains what the gap between the mouthpiece and leadpipe is.

Detailed Gap information

Additional information

Weight0.3 lbs
Dimensions3 × 1 × 1 in
Coupler Size

2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, Full Set (11 Couplers)


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Flex Couplers have been improved
over previous systems in three areas:

  • They are made out of Flex Brass Alloy. This proprietary alloy is extremely resonant and aids in the acoustic coupling (energy transfer) from the mouthpiece to the trumpet.
  • They have more mass at the main connection point to the mouthpiece. This increases the damping making the resonance easier to initiate.
  • They are held in place by a synthetic o-ring, not rubber. Rubber absorbs vibrations like the tires on a car. Our synthetic o-ring transfers the energy into the trumpet efficiently.