...from Clark Fobes’ website:

The barrel joint is an extremely important aspect of the overall acoustical design of the clarinet. It has a profund affect on modal ratios (pitch) and tonal coloration. We can think of the barrel as the "interface" between clarinet and mouthpiece.
FOBES barrels feature an inverted cone style bore and are designed to work in conjuntion with FOBES mouthpieces which have a medium large Kaspar style bore. Improvements you can expect with a FOBES barrel are:

1. Closer twelfth intervals

2. Slightly lowered pitch in the tones of the left hand, upper register

3. Focused throat tones

4. Increased resonance and response

These will work on and fit Buffet, Yamaha, Leblanc and older Selmer clarinets (pre Signature)