A "B" designation means that the outside dimensions of the tapered shank are 0.005 inch larger. This will increase the "GAP". Increasing the gap adds resistance in its own unique way, much differently than by simply choosing another backbore. Make no mistake  RESISTANCE is a healthy and vital part of maintaining a successful upper register! Be sure to check out our GAP CHEK tool for an easy way to compare the GAP measurement between your various mouthpieces and trumpets.
Try a "B" backbore if:
 High notes are easy at first, but soon tend to "wash out" or "airball"
 There is little definition to the notes above high C
 Low register is unusually free blowing
 There is nothing to "lean on" when coming back down from a high passage
Our standard shank size is designated as "C". We offer "A" through "E" size variations:  "A" is 0.010 inch larger than "C" (increases the GAP by 0.2 inches)
 "B" is 0.005 inch larger than "C" and is most often used to correct the typical gap problems as described above. (increases the GAP by 0.1 inches)
 "C" is the standard size shank which properly fits most horns.
 "D" is 0.005 inch smaller than "C" (decreases the GAP by 0.1 inches)
 "E" is 0.010 inch smaller than "C" (decreases the GAP by 0.2 inches)
It should be noted that sizes "A", "D", and "E" are made to order. If your horn needs one of these, chances are something else is wrong with the horn such as the receiver being extremely worn.
