All Fobes professional mouthpieces are designed to play at A440 with a 67mm barrel and A441 with a 66mm barrel.
These mouthpieces are designed to reflect the preference of most European players for long, open facings with wide tip rails. The resistance inherent in this design requires a slightly softer reed than my other mouthpieces. (Fobes suggest a Vandoren V12 3-3 1/2). With the proper reed strength these mouthpieces play with an extremely rich and dark sound, but are supple and responsive.